I ground the LED tips with the dremel this evening. Worked very nicely to help diffuse the light. Doesn't turn the buttons magically into flat-lit buttons, but it does increase the diffusion significantly.

Overall light output was reduced slightly, but that's OK because that's what I wanted it to do anyway.

I tried the drop-of-glue thing, but that pretty much just put the LED back to its original lens behavior, so I took the glue off and just have LEDs with flat-ground faces now. Looks great.