I'm surprised that no one has mentioned the use of pyro developers for dupe negatives. Bob Herbst describes an elegant process for making dupe negs for alt processes on his web site, www.bobherbst.com. I have been using his method for years and I feel it is the best way to create enlarged negs that I have seen. It is the stain of the Pyro negative which works so well as a UV light resist for alt processes.
The film Herbst mentions he uses, APHS, has been discontinued, and the film Freestyle says is its replacement (Arista-II Ortho film) is "not currently available" according to Freestyle's website.
So... what film(s) are you using in this process?
"What drives man to create is the compulsion to, just once in his life, comprehend and record the pure, unadorned, unvarnished truth. Not some of it; all of it."