Well, thanks for all the suggestions but it seems that what I wanted (plain old off the shelf alphabet in waterslide) is simply not available any more. I really don't want to start doing custom stuff just for a few words, never mind the problems with getting an acceptable white.
I understand the s.a. vinyl stuff can be slid around a bit by using soapy water, so maybe it's time to give that a try. Anybody done this? How hard/easy is it?