you could just by an extra diverter hose, and seal it... then plug your newly created "cap" onto the valves... would be a much better seal, and much less cheesy...
You could even get a bunch of the hoses, chop and seal them, and sell it as a "kit"...
http://www.realoem.com/bmw/partgrp.d...14&hg=13&fg=20