So, I spent $34 and bought a non C&P HK trigger housing for use on my PTR-93. I decided that for $34, it's worth giving it a shot. I have a Dremel, I have hand files, and I had time on my hands, so why not? Turns out, it was a pretty easy, if not time-consuming process.
I used the trigger housing that came with the rifle as a pattern, and I matched it as closely as I could. When I was getting close to being done, I switched from the Dremel to hand files to allow much slighter adjustments, and this turned out to be the key to a nice, tight fit with zero wiggle. It now feels far more firm and solid than the one that came with the rifle.
The only thing I have left to do is put in a pin, epoxy it into place, and then clip them. I have some extra HK pins coming in the mail and should arrive this week. I will then complete the process, and to outward appearances, this rifle will look like a proper H&K.
I'm pretty confident that anyone with the right tools, some time, and most importantly, some patience could pull this off easily enough.
Here is a photo of the finished project. I didn't take photos while I was doing it because I wasn't sure it was going to be successful, and also because I was more interested in just doing it right than taking photos along the way. As I just bought an Omega OM9, there's a good chance I'll be doing this again. When/if I do, I will definitely get photos of the process (although, to be fair, there are lots of photos already out there of this process).