I believe that Dan Miller has produced a quiver mount that mounts above the riser (bolts onto riser, both sides of channel). The quiver itself actualy sits parallel with the limbs, above the flight deck, above the scope's field of view. There is another model produced which is simular, but the quiver sits above and parallel to the flight deck. This was made by someone from the Excal site.

Someone on here whould have pictures of both for you.