You should be able to set the time the other player has to return the money, and, if the money isn't returned within the time, the lending player gets the money back and the borrowing player gets a debt, which they have to pay off immediately.
This will take a lot of work, especially developing the debt part into the atm and debugging it, and it might cause more chances for hacking. But I believe that this can be done. Please reply to support or to comment on any issues with this proposal.

Thanks,
tanglevine
