You have a great idea there, one I just might do myself - but your simply using the wrong product lol
Exhaust/manifold wraps are somewhat common on performance racing vehicles under the idea that keeping the exhaust gas temp as high as possible increases velocity and thus performance. A secondary benefit would be to keep the radiated heat levels down - in this case, away from your shins
For us, it should work quit well to quiet the noise a bit, I remember it took some of the "bang" out of the noise from my headers on my old truck.
For $10 it cant be beat, remember to look for motorcycle wrap as automotive may be too wide.
It's available in a variety of colors, some variants are self-adhesive (but I would use fasteners anyway)
Also remember the old equation; trapped water+metal=rust, but with the low replacement costs for these exhaust systems - I don't think that's a problem.
Hey - thanks for the idea man, I hadn't thought of this, but I'll prolly skip the can extensions