Really? No one? Is this a stupid question or something?
If you are the one holding the private key, why not program such a thing yourself. It seems to case specific for a wallet to support it anyway. I can't think of an overly simple way to achieve this but perhaps giving your "stakeholders" the price keybof an address with their stake contained would do it.
I'm thinking the best way for a stakeholder to cash out would be to exchange x% of the pot into bitcoin and then into a btc wallet. Is there a way to prgrammably exhange into bitcoin through an exchange or is this now getting too complicated? If this could be put together it could have real value for the crypto world