you'll need some very precise copper spacers to put on top of the RAM chips to fill the gap between the top of the GPU and the top of the RAM chips (since they arent even). only then could you use a heatspeader / pelt / waterblock to cool them all. HOWEVER, the BGA RAM those cards use probably doesnt get very hot at all, so cooling them in that manner is a moot point. play your fav game for an hour, the touch the BGA chips on the card to see how how they are. if they are only warm, you could just use
some RAMsinks.