I have been wondering if any one out there have added material to the little stop feet on button plungers to reduce travel? Not sure what i could stick in that tiny space.
I had a really funny punchline worked out, but I've withheld it on account of David Foley's wife probably not appreciating it that much.

In seriousness, you could probably use a little blob of epoxy or JB Weld. It could be filed down to fine-tune/equalize travel. Depending on the composition of the buttons (I think they're ABS, but could be wrong here), you could alternatively use a suitable plastic welding compound and thin sheet stock to shim the feet.