Not sure if your problem has been answered yet, as I haven't read the entire thread, but I feel like putting in my two copper pieces...
I personally agree with the OP with the Magic Items being used too often in a cheesy manner to grant extraordinary abilities, so my suggestion is to not bring out more magic items, but rather to bring out maybe an NPC that can teach the Fighter a thing or two about how to use the Sword-and-Board. Perhaps an NPC who is a knight who, after some RPing between him and the Fighter, gives in and teaches the Fighter a sword technique that can remove either a daily usage of a spell or a use of that spell slot at random from an enemy caster, or maybe two on a critical hit.
Or perhaps maybe the Fighter isn't all about damage as we can tell, he is a gallant figure, so maybe his role isn't in cleaving foes in half, but in making it much easier for the foe to get cleaved in half. So like I said about the destruction of prepared spells, or maybe the Fighter learns another technique that can remove X amount of Damage Reduction for a short time, or perhaps another one that can dispel spell protections from other casters.
In this case, I don't think anything in any splat-book or rule-book will be able to help you, so like you were saying, we need to make our own rules. I guess all I have to say is use your imagination, and find things that hinder the other's ability to bypass encounters, and make it so the Fighter can "break the hinderance".
Again, Sword-and-Shield is not for damage, but more of a protective and support style, so think about techniques maybe not just for the sword but for the shield as well that can help. Also, don't make those techniques require feats if it comes to that. Yes, its not a "balanced" solution, but in the scope of a game like this, the only "balance" needed is the kind that ensures that everyone is contributing to the group in their own way. Then if all the players and you are having fun with this "unbalanced" fighter, then "balance" is a pretty meaningless thing. I'm sure you knew that though, but I think it bears repeating.
I'll end this post with a quote I think by Gary Gygax, if I'm quoting someone else, please correct me.
"In the end, you don't need rules". Rules are a tool to ensure everyone is playing on the same kind of field. If those rules are no longer doing that, then those rules are no longer useful. Make your own rules in that case.
Good luck!
