Dimension Theory is an expert on all things light and HDRI-related, and I use his products regularly. The other day he said something extremely useful on the forum:
You can actually use mesh lights without them being visible in your scene. Set the cutout opacity to .001, then set the mesh light settings as normal. They will not appear in the scene or in reflections.
This is life-changing info for me, because I use mesh lights a lot; they really look the best on human skin in most circumstances so I consider them mandatory in most scenes. I can confirm that this works because I've tested it this weekend.
Test it yourself, use it, pass it on. Just don't credit me with the information. I never would have figured it out if he hadn't mentioned it in a post.