I think it would be very difficult to do what you are suggesting, given the back focus. I doubt you'll be able to find a 4mm adapter that would work, or even to manufacture one would be hard if not impossible. I recently mounted a cheap minolta lens on my 383L with a custom made adapter. The lens backfocus is 44.5mm, and I was not able to incorporate the filter wheel into the mix at that short distance. What I did instead was find an adapter that reduced the front threading of the lens (49mm) down to 1.25" filter threading. So I can use my Baader 1.25" LRGB filters on the front of the lens. This is certainly not ideal and I've not tested it out for things like dew formation on the front filter, but I'm optimistic.
If you find a solution in which you can use the filter wheel too, I would love to hear about it.