Double post: I had an idea for the Little Sister playertype/bot. It could not move or attack and would not get hurt but players could pick the player/bot up to move.
You could look at the Jockey script in ZAPT for the picking-up part.
Also: Wouldn't a custom HUD be cool, that shows your weapons/items with special icons?
ZAPT does that, it recognises a weapon in your inventory and places it by your health bar :o
EDIT: I'll be trying my hand at the Chemical Thrower in in about 20 minutes, gotta fix up something.