Two approaches that may work better -
Method 1 - Use the bag as a peapod. This will only work if you have a 2 way zipper on the bag. A little more confining, but you have your TQ and UQ all in one.
Method 2 - Four Grip Clips
attached at the 4 "corners" of the bag with cordage run the same way a UQ would be run.
Pardon the basement shot, it is raining here.
The second method is the one I prefer. It actually has the same exact feel of a UQ (because it is functioning exactly like one).