I have an idea. Go get some huge hose clamps and some small metric nuts. I think you need three nuts and three large hose clamps. Have your local welding hillbilly weld the nuts on the hose clamps, one on each, not too far away from clamping / tightening mechanism of the clamp. This will allow you to hide the clamping / tightening mech. behind the heat shield once installed. Slide the clamp assembly over the muffler.
I'd think of something to put between the clamps and the muffler so you don't garf up the muffler surface with the sharp edges of the clamps. Like a thin layer of fiberglass mesh or something. Anyways - orient the nuts such that you can install the stock heat shield. Install it - make sure the thread depth os OK so you don't dent the muffler body by tightening the heat shield bolts. You might need a spacer or washers. Go ride.