What you're looking for here is (as far as I can tell) a way to promote character flexibility about the magic items they receive. Transfer Enchantment, and simply the fungibility of swords/axes/etc. in the first place, makes that easy for one set, but not for the other, because of how distinct implements are.
But my first question is this: why does "The staff the tiefling was holding" have only one tagged function? Why, in your campaign, is a power which functions only for wizards present at all, if you have no wizards? Remember that in exception-based design, what it does in the monster's hands is supposed to have no necessary relation to what it does in the PCs'. Yet for magic items this seems to be typically forgotten. (Obviously, for style reasons it's usually similar. But it need not be exactly the same.)
Extrapolate that. The staff that did X in the NPC wizard's hands can't do X in the PC warlock's hands, because X is irrelevant to the warlock. Fine. What's the closest analogue you can come up with that won't be irrelevant to your warlock?
If you choose to require facility with that implement in order for it to not be irrelevant, that's fine; the Implement Proficiency feats exist for that reason. But that doesn't stop it from being irrelevant once they take the feat, hence the other suggestions in this thread. If you want the item to be potentially relevant to your warlock PC, then the onus is on you to further specify how this object can become relevant.
Ruling that you get to use it with your best mental stat is one approach, and not a bad one. But that's a special case of the general one. They're your magic items.
Try to think of it like this. Every enchanted implement in your game should most properly be listed something like this:
Orb of Warping Space
Implement, Orb
Wizard (Daily, Free Action) - Use this power when you hit with an area or close spell with this implement. Note the squares occupied by all creatures successfully hit by this attack. Until the end of your next turn, the next time you use an area or close spell, those squares are added to the area of effect.
Warlock (Encounter, free action) - When you apply your Warlock's Curse to a target, apply it through this item. Until the end of your next turn, you calculate line of sight, line of effect, and range starting from that creature instead of from yourself. You cannot target the creature out of whose eyes you are looking using this effect, unless they actually look into a mirror or the like.
Swordmage (Property) - You may affix this item to the hilt of your bonded sword. The sword functions as an implement using the higher of its own bonuses or this orb's bonuses, and is otherwise statistically unchanged. When you invoke your aegis power, in addition to the usual effects, you may teleport the ally targeted by the triggering action two squares.
Bard (Daily, Standard action) - Throw this item into any square you can reach with a light thrown improvised weapon. (If actually thrown at a creature, it has a proficiency bonus of +2 and applies its enhancement bonus to the attack and damage rolls.) Until the end of the encounter, when using a bard power you have line of sight, line of effect, and range to any creature in the same square the orb, regardless of the normal range of the power.
... and so forth. What does X enchantment do that is cool, in the hands of the relevant PC? This is easy for weapons, less easy for implements... but as shown above, it can end up cooler for the reinterpretation necessary.
(Also note that in my example, only the Wizard's usage actually requires that it be usable as an implement. Loosen the rule that you can't use an implement's power if you're unable to use it as an implement in general, and you still have a reason to want Implement Proficiency - so you can use the enhancement bonus on it - but you can still get utility out of it regardless.)
And, of course, since you're doing this for a specific campaign, you don't need to design all those usages. Just the relevant ones to your players. Heck, if you want to make it interesting, do something along the lines of the swordmage's ability above, and let it be useful for the martial types, too, so they get to argue over it. Equivalent backward-swaps with weapons are also perfectly possible. Let the wizard cast spells through the Flaming Longsword even though he's not an Eladrin Sword Mage or similar; he won't get the enhancement bonuses until he gets proficiency, but maybe he can still use it to light his Magic Missiles and Cloud of Daggers on fire.
