They would need some way of coordinating signing the transactions but that's not terribly difficult, could be through a shared cloud database or such. Any competent developer could build it easily. Another way would be to have multiple smaller proposals with individual owners. Eventually there may be a smart contract solution.

I'm doing it now but I have no particular attachment to it, and would be happy to hand it off. I make no profit from it and in fact it costs me money. The current setup is more of a proof of concept than intended long term steady state.