All, thanks for the lively discussion about my dilemma. I think I'm gonna back to the drawing board a bit to avoid this rather crappy pattern. I personally hate entries that are both obscure and not inferable from the crosses. e.g. WELLMAN, WALLOON, and WILLSON. Even if I had 5 of 7 letters, I still don't think I'd be able to get any of those 3, no matter how straightforward the clue. Just because editors have allowed these entries in the past doesn't mean they should have, IMO.
If I was intent on keeping my W??L??N word, I would definitely stick with WALLS IN. It's inferable, despite also being clumsy and awkward.