Following your recipe mostly, I built the module and loaded it. It didn't complain and I'm posting this via the result. So far so good with that degree of minimal testing.
Just a couple of notes wrt to the build. I used the Debian patch set you pointed me to, since it appears to be maintained and I have reasonable regard for their process. 21 patches, and some of them are stacked in the same files so a few .rej files got generated. I looked at them and they looked sane, so I built with the results of the patch. I had to make one change to get the build to complete. In lib, the Makefile is expecting wlc_hybrid.o_amd64, but the packaged version has wlc_hybrid.o_shipped. I renamed it to wlc_hybrid.o_amd64 and the build completed without errors.
Thanks for your help.