Just as a thought, if all you're having trouble with is the "sword" part of swordmage, then try this:
- Pick an implement (or implements) and/or a style which implies same. For my example I'll pick "Bonded Guardian" - player wants to play a slave who is magically bound to another PC ("the Boss"). His implement is a slave collar; he has had one hand removed (thus netting the same effective number of available hands as the swordmage); the slave collar does not take up a neck slot in its own right, but he can flavor any neck slot item as properties inherent in his collar, along with its implement-enhancement bonus (as though they were two items, one slotless and one neck slot, occuping the same physical space). Use the Magic Item Levels as Treasure rules extensively when handing him stuff for his slave collar.
- Pick a new stat set if appropriate. For my Bonded Guardian let's say I decide to make it Con-primary, with Wis (loyalty and willpower and intuition) as my secondary stat, and Int (basically 'cause it's still fundamentally Arcane) as my tertiary. Mentally find and replace Int with Con, and then (depending on build) Str/Con with Wis, and Con/Str with Int.
- The easiest of the three Aegises to reflavor is definitely Shielding, so let's encourage that. Second would be Ensnaring, which would work OK (drag them away from Boss). Assault wouldn't work for the Bonded Guardian concept particularly well, as I'm seeing it here. So remove that option (since you're probably doing it for a specific PC anyway), and thus your mapping is necessarily Con to Wis, Str to Int.
- All weapon powers become Melee touch implement powers. Pick (or ask the player for) a default "weapon" for the conversion. Longsword means that [W] turns into d8s, the "weapon" keyword turns into a +3 accuracy on the power's hit roll. Broadsword does d10s and +2; if he's willing to spend a feat on "Bastard Bloodline" (i.e. Weapon Proficiency Bastard Sword) then it's d10 and +3. Other than to upgrade from either non-feat variant to Bastard Bloodline, he can't change his mind after the campaign starts; this is a conversion baseline you're looking for, not a weapon-of-the-day choice. Case by case you may want to drop the +2/+3 and convert from targeting AC to targeting a NAD instead; this'll depend mostly on how you opt to reflavour specific powers.
- Swordmage's Warding would work fine as written, reflavored into (e.g.) Nimbus of Slaves. Keeping his still-intact hand free would have the flavorful result of a combatant with entirely empty hands, which is neat. You could tweak the flavor slightly by having the "if you have a free hand" be +1AC for you and +1 for The Boss, instead of +2 for you.
- Aegis of Shielding or of Ensnarement would also work fine as written, but again I'd tend to tweak 'em a little for flavour reasons. Make the origin point for the marking action The Boss, instead of the slave himself, for example; if you're within 2 of The Boss, then I can mark you. [Maybe the Boss can use a free action to order me to protect someone else, at which point the marking origin passes to him instead.] Tweak the effects slightly to priorize defense-of-one-person instead of defense-of-all, again in keeping with the flavour; say, the Shielding benefit blocks 7+Wis HP on attacks on Boss, 3+Wis on attacks on his allies, and if Boss designates another then that other and Boss both go to 5+Wis until the designation is removed. Or, for Ensnaring, if it's against Boss then I can make a Wis implement attack roll, and if this roll beats their attack roll on Boss then I ensnare them as an interrupt instead of as a reaction... but if it's against anyone else then it stays a reaction and they don't grant CA to my allies, like they usually would.
- Swordbond is basically an RP benefit anyway, for the most part. Turn it into Slave's Bond, where I always know the direction and range to The Boss, instead.
- I'm seeing this one as a lot of "intangible light show" style effects (there's a constant barely-visible flow of energy from slave to master; this energy lashes out and colours itself differently depending on the attack)... which would mean that when reflavouring I'd also retype a fair number of the elemental stuff (especially Fire, Cold, and Acid) into things like Force and Psychic. Having a lot of Force damage stuff would be fairly unique and fairly flavorful here.
- Balance on the fly as you go, often by tweaking the granted magic items and/or converted powers. If it's proving noticeably overpowered, use the master-slave bond as a disadvantage - occasionally have a condition inflicted on the master flow down the link and hit the slave as well, for instance. If it's noticeably underpowered, use the link as an advantage - maybe once per encounter (or at will if it still needs a tweak), when the master is called on to make a death save the slave can make the save instead.
There.
Presto - a new Arcane Defender. And a nifty one - I'd play that!
Similar things could be done using one of the other defenders, retasking to Arcane as part of the reflavouring.
Maybe a fighter-equivalent done up as a Fate's Fury, one who actually channels power from the presence of risk and death; his [W]s convert into a variable based on some external information, such as the nominal level of the fight (from 2d8 for a Level+4 encounter down to 1d6 for a Level-1 encounter), and he marks using "Free action: Grant an enemy +1 to attack and +1/2 your level to damage until the end of its next turn. That enemy is marked by you until the end of your next turn."
Or a Warden-equivalent based on madness (Opener of the Way?) with strong Far Realm ties, whose 'Form of the X' powers become triggered insanities rather than physical shifts; increase their power a bit but give them all serious downsides as well. Whose marking and difficult terrain are all about the reality leakage that constantly surrounds them, and whose Font of Life has self-warping effects (some good, some bad) when used.
