I imagine you could have some contract that interacts with ecash, based on revelation of a blind signature. Similar to a HTLC.
I have actually written up some ideas for a system based on something like this that I called "chaumian coupons", but I would have to go through my notes to find it.
I have actually written up some ideas for a system based on something like this that I called "chaumian coupons", but I would have to go through my notes to find it.