Perfect example then. When a miner chooses the Slush pool for one version, any blocks found using their hashpower will have that version. I assume that Slush pays people in both "effective" pools from rewards earned by each pool (so everything is shared). So in order to reward a Slush pool participant for choosing one of the versions, I would have to find some way to get a bitcoin address for that participant. Kano's idea of asking is great, but can't anyone claim to be the person who mined a block? How would such a claim be verified?
An acclaim board is often used to tell you who mined the block by many pools like kano.is though the pool is under zero obligation to tell anyone any details whatsoever. The pool owner is the ONLY one who has ALL the details beyond a shadow of a doubt.