I don't know much about gambling but is it not common to set for yourself max bets so your pool of cash doesn't deplete like you do when buying stocks or trading options so you can leverage up or down. I know it's a little different, but there is a similar principle.
Maybe only allow people to spend 1/5 their pool of cash per bet so it never reaches zero
Maybe only allow people to spend 1/5 their pool of cash per bet so it never reaches zero