I make my own exhaust systems fron copper tubing fittings (the ridgid type) for the muffler I simply use plumbers tape (the metal strap used to hange pipes). It has holes punched down the length and is about 1/2" to 3/4" inch wide. I simpley twist the tape into a slow spiral and insert it into the copper fittings as I solder them together. This soes not give too much back pressure but definately has a dampening affect on sound. This method allowes me to run the exhaust right where I want it using elbows and "T" fittings. First one I did was on a ST3000 and it sounded great.

You should be able to just stick a twisted piece in you existing pipe and fasten it in with a screw if it is long enough.

Hope this helps