I think I figured out a workaround for the problem. In the Guillaume script, I just took out the default shield slot, created a shield that was technically a weapon, but had no attack and boosted def just like a shield. Now, the player can use a shield and sword or a two-hander without a shield. They will still be able to dual wield, which I didn't really want, but I'll take it. Plus, I could create a couple of "shield bash" skills for certain shields, and that would be pretty cool.
Not the ideal fix, but I'm satisfied, as long as no one pipes in and says, "Whoa, that will mess up the whole time-space continuum to have a "shield" in a weapon slot!