There is no way for a game to be guaranteed or provable fair to investors.
I don't understand why you would put yourself in such a sticky spot on purpose?
Important: There is no guarantee to investors on provably fair sites because the owner can still play within the rules and "beat you fairly". These sites are only proveably fair to players... NOT investors, it isn't possible to prove. Unless I'm outside on something new.
Actually there is, and bustadice has it implemented!
I made a high-level overview of how it works here:
https://gist.github.com/RHavar/285c295f7906e03369cd66580a1b5f45 and you can check bustadice for the actual nitty details. But the tldr; version is that there's two server seeds. I know one, Daniel knows one. He can't "play against the house" because he doesn't know the seed I'm using.
I do think you're right about putting myself in a sticky spot though. But more due to me being one of the 2-of-3 key holders for BaD's cold storage. I originally did this because as I can audit the game results, I could check and see if there was any funny business, I can refuse to process transactions from cold storage.
But after thinking a bit more about attack vectors, I realize there's something I didn't think of earlier: Daniel could fake a bank-run. Maybe intentionally get some bad publicity, then act like almost all investors have divested (e.g. 90%) and then he tells me to sign the transaction, because he needs to pay investors back. Since I can only audit game results, and there's no cheating on the game results there's nothing I can say. And then instead of paying investors, he just puts it in his pocket and exit scams.
So I believe I can state with a high amount of certainty that the stats on bustadice.com are legitimate and importantly all big investor wins are totally legitimate.
And while there's a lot of benefit in Daniel not being able to undetectably rip off investors, the cool thing is actually the guarantees I provide Daniel. Let's say I got hacked, there's nothing I can really do (by design). And if Daniel got hacked ... just knowing Daniel's server-seed is not enough to predict games, so the attacker would
not be able to undetectably cheat. Which I think is a
huge deal. I remember always my biggest fear running a casino is that my system got compromised and someone was able to feign being lucky whale(s) and just draining the site dry.
Anyway, it's a super cool system. I've even considered offering it as a service (auditor-as-a-service) but I've been a bit busy to build such a thing.