HAH! I came back to this topic, and it took me forever to find, since I *have* a suggestion!
The Cosmo Kama Sutra book (Not sure if EF sells it) doesn't show any nudity. It uses illustrated, genital/breast-less figures to show the sex positions.
I'm proud of myself for this, by the way. So yeah, that's the only book I've found that doesn't.