What I do at Just-Dice is risk up to 0.5% of the bankroll per bet, so investors can play it safe with "half Kelly" if they want to, and then I allow them to use up to 25x "leverage" by declaring an "offsite" amount for those who wish to risk a full Kelly, or limit their counterparty risk.

It turns out that on average investors are 16.8x offsite-leveraged which is likely too much for lots of them, but that's their call. I don't see a good reason to force investors to always have over 1% of their coins at risk to a suitably motivated multi-accounting whale when the house edge is 1%.