I would start by not forcing the fighter to take medium armor, heavy armor or shield proficiency at 1st level; convert those into bonus feat slots. That way, a fighter who wanted to go down a different path could do that more easily -- take Improved Unarmed Strike or whatever.
I toyed with this idea too, but seemed unbalancing. I mean say I am a rogue,monk,ranger, build for one level of fighter I get 4 extra fighter feats. I don't want armor prof and a one level dip for 4 feats sounds to powerful.
Normal bonus feat+(1) from tower shield+(1) from heavy armor+(1) from medium armor