My track insert is fairly hefty--aluminum, I think. I'd consider drilling right through it into the mast
Would probably work. The track insert is just an aluminum extrusion (I wish I had a photo of mine when it was out, but I don't). In section it looks like this. My guess is the flat part is something less than 1/8" thick
It slots into a section of the mast extrusion that looks like this:
Its mostly designed to be a cosmetic trim-piece, I think, and probably wouldn't take a lot of load, but if the fasteners went through into the meat of the sail mast itself, should be fine.
NOTE: there are likely wires (electrical for mast lights and coax for masthead antenna) inside the wire-channel behind that insert, so drilling through it runs the risk of drilling through the wires...
If it were me, I'd consider finding (or making) a plate like the one that supports the boom vang, fastened to the "meat" of the mast section on either side of the track.
You could drill-and-tap the boomkicker fitting in the center of the plate, and then fasten the plate to the mast. Would spread the loads out nicely. If I understand the boomkicker design, the loads would mostly be compression (as opposed to the vang, which is in tension), so it might be overkill, but... perhaps a cleaner install.
...and, yeah, definetely don't chuck a tap into a power-drill. They're brittle, they break, and it's a major pain in the butt to drill out the remnants. Don't ask me how I know (grin). A standard T-handle is the right way to go.
Edited to add: thread locker won't keep stainless fasteners from interacting with the aluminum of the mast. TefGel or Duralac is good stuff for bedding the fasteners. Duralac might be better if thread-locking is required, as it "sets" into a putty-like state, where TefGel remains liquid-ish.
$.02 (probably worth significantly less)
Bruce