Race fairings? Slip-on wouldn't be enough... these things are designed/formed to fit over race exhaust without the fat CAT.... a cheaper solution would be to buy a Y-Pipe and get it welded or bolted on to the stock headers.
I bought an exhaust from MJS Performance. It's really the stock exhaust modified and welded as a race exhaust, eliminating all the CATs. It isn't super race performance but a cheap solution to a $1,000+ race system (I think around $300 for a 600cc). And they'll buy back your full stock exhaust for $80-something. They also sell the Y-pipe if you have someone good with cutting and welding.
http://www.mjsperformance.com/
But you'll need a power commander/bazazz if you don't already have it.
So maybe fairing modification would be cheaper
Yup I have a fiberglass race fairing but stock exhaust with huge CAT. Dave was going to give me a used exhaust but it didn't fit on the bike right. My buddy who sold me the bike said we can just mod out the part on the bottom that the fairing bolts onto and the bottom fairing should fit after that.