Just got one of these for my rear tyres, especially the one on the rear brake side. :-\
I have been looking for the inner tubes with the bendy valve similar to the one you can get for the front wheel.
But this works ok. ;D
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280452215414&ru=http%3A%2F%2Fshop.ebay.co.uk%3A80%2F%3F_from%3DR40%26_trksid%3Dm570%26_nkw%3D280452215414%26_fvi%3D1&_rdc=1
....they do work, Kurt and myself have both used them.
This method is free though :D;
http://c5alive.co.uk/forum/index.php?topic=247.0