You could put an aftermarket baffle in the pipes. There are many baffle options out there based on the diameter of your pipes. Try sites like JPcycles and motorcycle superstore to find them. I'm not sure what the diameter of the stock pipes are though. Any help?
Most aftermarket baffles are insterted by either drilling a hole through the side of the pipe and locking the baffle in place with a nut and bolt or welding the baffle in place. Our own Dinqua even goes into how he inserted an aftermarket baffle in his pipes: