Dan Erlwine suggests taking filings from past "nut jobs" and packing it into the nut slot and adding crazy glue as you state above.Pete Moreno showed me this great trick for this problem....you take super glue, put a few drops in the slot that is too deep, then sprinkle baking powder over it, pat it in.......it turns rock hard almost instantly! then sand and file to desired height.
it works, i have done it on a couple guitars!
LOL!Don't laugh, but the fastest, easiest, and cheapest way I've accomplished this is to fold up a very small piece of aluminum foil, place it over the nut slut, and then tighten the string to force it down into the nut slot.