Well, here are a few ideas, the first two will take more machining. Oversize the hole by 1/4 inch give or take, then thread both ends. The end caps would be at the same diameter now and each have the set screw. You would of course have to adjust the length of the current design to allow for the end caps. You could then machine hole patterns, this design is similar to those already out there.
You could also keep the same design you have and drill a hole pattern in your current shroud design.
One other idea I had was to use some slightly larger bar stock to get more of that suppressor look. Just some ideas to play with.