Something I mentioned on IRC:

It would be nice to offer people some compensation for their shelved shares.  That way, you can get paid immediately by selling your shelved shares to another buyer.  Similar to selling bad debt, in the real world.

Each shelved share is worth more, the closer to the top of the stack you go.  Therefore, you would want to give some indication how close to the top of the stack are the shelved shares for which you are bidding.