Well, I have a silencer that I bought along with my catback. It is basically a plug with a one inch outlet that sticks into the muffler (CorkSport mufflers are N1 replicas.) Maybe there is something like that availible for yours.

Steel wool is used as a packing in a lot of mufflers, if you could find a way to hold some of it in it might help... but I wouldn't try it. Whatever happened to your stock exhaust?