can't you do the fake eating thing?
You put the item in your hand, cup it, put it to your mouth, begin to chew and make mmmmm noises, while the item is still in your cupped hand, turned away and lowered to your side. You distract them with your it's so yummy face and you either slip the thing down the back of the sofa, or into a pocket or even just keep it in your hand and after a few minutes of mmmm-ing
you need the loo.