There isn’t a great way to do this at the moment due to the fact that you can’t save data between rounds. I’m hoping this comes soon because it would really help a TON of people with map creativity.
There may be some real round-about ways to do this. I see your attempt at the Session map. You probably realized it resets after each Round. I think this is in the request queue for Session to remain between rounds. I haven’t been able to find any device workarounds at the moment to persist the data. I actually decided to go the “Player Vote” route on this issue instead of random. :-/
If I come across a solution, I’ll definitely post something.
-MF