My suggestion is a fairly simple one, or at least I hope so, for the purpose of making some ranged builds a little better on their own.
A feat which stops enemies getting attacks of opportunities when they're in melee, when you're being guarded. It is a bit painful, when you're in an enclosed area, where you can't kite enemies, and you're relying on someone with a shield to protect you, but the enemies ignore them to slam you into the ground, if you dare to shoot.