I have been thinking about this myself jarvie and have come to the conclusion that you need to implement it in the steem monsters protocol - and that needs to be done on the steem monsters side.

There would be one way how this could be done on a user level, which is by using a trusted middleman, who takes a security for the cards and than lends them to the person to whom it is supposed to be delegated. If the card is then not returned in time you would get the money instead. But this is ot really delegation but more of a pawn shop for monsters…