The honest answer we've never tried ourselves but the information from a couple of Trade customers is that it doesn't really work very well. It'll just about fits but it ends up taking a slice of plastic off the handbrake cover..
If you don't yet have a drivers seat swivel we recommend the RIB one - they do not need the handbrake modification so they are easier to fit... and they work very well with the double seat swivel. They are a few squids more expensive but easier to fit, and they just work!
Update: just come across a thread in the T5 forum showing how to make a sportscraft handbrake mod with our double seat swivel: http://www.vwt4forum.co.uk/showthread.php?p=2325980