I looked at this too Tony but luckily the Donington track day I got onto in August 2012 was full noise. They ahve about one a year! There is another solution though that I reckon you can do with three 6mm holes at 120 degrees around the reverse cone so as not to have to butcher the pipes. If you get some decibel killers, 2" ones that are about 8 inches long, I experimented by wrapping an extra 1mm thick steel strap around the wide end so it fits snug in the reverse cone exit. I then drilled the strap and db killer at 120 degrees, 10mm holes and fitted three blind hole threads - like hollow threaded pop rivets if you now what I mean?
Then, with the holes in the mega cone, you can gently insert the baffle and fit the top 6mm bolt through and into the db killer end to attach to the threaded insert. Ince on is in, add the other two and slowly tighten each by the same amount. It creates a kind of dynamic tension that keeps the db killer straight down the middle of the pipe. Keep going till all three are nice and tight et voila!
Biggest cost is the db killers, I think mine were about 17 quid a pair but then it's just time. If I can find mine tomorrow I'll show you a pic. Of course I haven't had to drill my cones and fit these permanently yet as I had the full noise day at Donny so haven't proven they stay put but as the three bolts cause opposing forces and you can always use allen heads and lockwire them, I'm pretty confident it'll do the trick...remove then when you want more fun! :-)