Well the main thing is to not allow alts to interact with their main accounts in anyway. Technically when they spin, they increase the jackpot size, so if they go back and spin on their main account and win the jackpot. They are in-turn transferring some degree of coins between accounts. Which is of course not allowed.
Could make it one or both of these:
Tradebanned people are not allowed to win/see the jackpot, and/or they can not increase it. So they can still spin and win stuff, but not anything that involves other people.
Could make it one or both of these:
Tradebanned people are not allowed to win/see the jackpot, and/or they can not increase it. So they can still spin and win stuff, but not anything that involves other people.