If you want to keep the concept of carrying a shield instead of having one floating around next to you, you could homebrew a shield enhancement that costs the same as an animated shield, but instead says something along the lines of "any weapon being wielded in one hand by the user of this shield is treated as being wielded two handed for the purposes of power attack, strength bonus to damage, and (any other important part of two-handing a weapon that I'm not thinking of at the moment)."