Why don't you force players to sign a message from their cold storage addresses confirming they actually have the coins they claim to have. Then only count the lesser of the amount of coins that are in those address(es) or the amount they claim to have (they may not want to use all of their cold storage for the bankroll).
This would prevent people from lying about the amount of coins they have and would keep the bankroll more "honest"
It's been stated over and over. It doesn't matter how many coins they have. Some might want to invest but hold Bitcoin instead. That's their choice. What matters is how much risk they are willing to take. No more, no less. If you have 1 CLAM and want to act like you have 100, that's your choice. But if you lose that CLAM due to a whale getting a single good roll, that's your own fault.
Signing messages means nothing because nobody cares how many coins you actually have.