OK I figured this out. You need to go in game, then alt-tab out to a terminal and enter the aforementioned xrandr command and alt-tab back into the game. It does not run with all games (The Witcher 2 and Diablo 3 did not respond) and sometimes it causes flickering, but it works (For instance in Bioshock Infinite).
I hope AMD will update the amdgpu-pro driver at a fast pace to iron the kinks out, but now at least I'm hopeful that someday we will get feature parity with the windows counterpart or close to it. Good Job AMD!