That’s a genuine 2 mm carbide end mill, poked 1 mm into the key cap, snuggled right up against the front edge.
Two epoxy dabs and some wiping later:
The careful alignment on the F key tells you I did it first; obviously, I should make better fixtures.
The holes could be slightly larger and maybe slightly deeper, but the bearings feel just right.
Indeed, they work so well a ball now distinguishes the far-flung Delete and Backspace keys:
Now, to see how long the epoxy lasts …