OK, I think I got it sorted.
Sort of.
I used the DREMEL.
...and a few files, and a dental pick, and a screwdriver, and a pocket knife.
Under closer scrutiny I was able to peer through the gap between the button-lever and the holster.
There, I could see the trigger guard was coming noticeably (but not hopelessly) short of engaging the button lever.
I got out the DREMEL with the carbide mill bit and went at it.
It was really close quarters as far as getting access to the area that needed material removed.
Here is where one of those wand-type attachments might have been more nimble for the job.
I was able to cram the dremel into the holster just enough to reach the button and start cutting on it.
Actually, I'm not sure I would call it "cutting," since the plastic just heated up, and melted into a globby burr on the engagement-face of the button. That's where the files and the pocket knife came into the job. Had to use those to carve the globby burr off the engagement face.
After about a half-hour of carefully going at the plastic part with the dremel, and then making fine adjustments with the other tools, the gun finally CLICKED into place. HOOORAY!!!
The pics show a before-and-after of the work on the engagement lever.
The pic with the red arrow is the "before" pic.
The funny-looking part at the bottom is a plastic dingus that is supposed (I guess) to keep some tension against the trigger guard to mitigate any rattling of a gun that may fit a bit loosely in the holster.
I omitted that part on this job, since the gun really fits with a "smoosh-fit" into the holster, and there is absolutely zero chance of it rattling in the holster. I still have to push the gun into the holster with deliberate pressure to get it to lock into the holster. I can't just drop it into the holster as I am able to do with this same model holster and a Glock.
I guess I'm OK with how it turned out.
After all, its a $25 holster (Palmetto "clearance" item).
I can live with that.
I'd still like to get a nice leather pancake holster that FITS RIGHT for the 92S.
If anybody knows of nice leather concealment OWB holsters that they have actually tested, I'd be obliged if you would post.