Just buy the B4 rear anti roll bar kit,and to mount it cut a slot in the bulkhead with a junior hacksaw,then take a small angle from the rear bulkhead(one on each side),it only takes a few secounds with a Dremel type tool.The only other thing is to shorten the links so the two plastic ends screw up to one another.The kit is about a tenner and available from DMS or MK Racing-(you get three different thickness rollbars in the kit to choose from).If you look back through the old topics on here theres even some pictures and while your looking theres always a good chance youll see plenty of "other" things that will grab your attention,a marvellous bunch of people on here with plenty of help to hand!!
(Just had a look myself,go to page 3,and theres a picture also)