I know it's possible to use scripts to attach scenery objects to special nodes on bipeds (characters hold/manipulate objects in cinematics) and I think it may be possible to do with named weapon objects as well. But come to think of it I've only ever seen these objects attached to the right hand, which is the same hand a unit's weapon gets attached to if I'm not mistaken. It may be that a biped can only have one such special node.
I'll have to experiment with this.