I can almost do this. I am one $30 non-existent carbide router bit away from heaven.
The carbide burr in the photo
above cuts through, but really isn't suitable for something as soft as wood, it clogs and burns, though will clear it out eventually.
I found an old HSS 3/4 inch diameter straight plunge router bit (shaft 1/4 inch) that started off as 3/4 inches long. I took it down to about 3/8 long on the grinder. It cleaned out the first hole in about 15 seconds. About 5 seconds into hole number 2, it was too dull to continue, having hit enough glass to render it useless.
So what I need is a short plunge bit but in carbide. Which seems to mean that I need to find a carbide grinding wheel
(I believe the green ones) to modify a 1 inch long stock carbide bit down to 7/16 or 3/8. Another possibility is a box slot bit - remove the bearing and grind away the bearing shaft. The second idea is back to grinding HSS (I don't think wood bits are solid carbide), so it is the one to try first.
Maybe I am being too fussy in wanting to undercut the holes such that the eventual epoxy
(approximate) torus is trapped between the 2 skins. I still like the idea of the epoxy
being mechanically locked in by more than just a bit of roughness from the hole saw.
That is my report for today. Sigh, sometimes I just can't seem to get started. Stuff like this is evidence of the rule
of 3 times the cost and 3 times the time ...