Quote -  I'll have a set of matching poses. So the user loads the pose on the character first, then loads the pose for the prop. 

 Is that possible? I swore I remember trying to save prop poses and they wouldn't work. Maybe I didn't have a figure in the scene.

That is possible. This requires, that the sword's parent is some part of a figure (as it would be the case for a smartprop). The smartpropped figure is practically handled like a body part in this case. So the technique that would apply is the same as the one used for partial poses you can find here and there; you write a pose file only for specific body parts (which can be arm, leg, or sword for that example).