i know this isn't what you want to hear, but the most dramatic improvement in tuning stability i've experienced in a non-Floyd guitar was when i had my guitar's bone nut replaced with a graphtech trem nut. other materials such as regular graphite or slipstone will likely work as well.
in the past, i used to write on the nut slots using a #1 pencil. hehehe, halos pagalitan ako ni Jun Castro when i persisted with the practice, and with good reason. in the short term, my strat did stay in tune pretty well despite a good amount of whammy abuse. but the pencil lead/graphite gunked up the nut slots as time went by, dulling the sound of the open strings and making it even more difficult to stay in tune. i suppose you can apply pencil lead then clean the slots up often. kaso hassle naman.