What you do is have the material assigned to the blocks in WED and you assign the bump map through code. Visit here to get the code:
You'll have to alter my dot3 texture names and your material name so that it'll work

http://www.conitecserver.com/ubbthreads/showflat.php?Cat=&Number=448727&page=2&view=collapsed&sb=5&o=&fpart=1#448727