OK--one more over the top solutionA coach once (not more than half in jest) suggested putting tacks in the heels of my ski boots. When he said that would keep me forward, my impression was that he was speaking from experience.
If you are having huge difficulty changing your ingrained habit, you can tape something uncomfortable (not a tack--say, a pebble, or a short stack of pennies) to the underside of your heel. Then ski a moderate slope, staying completely forward the whole time. When you've got that down, go to a steeper slope and repeat.
You will get immediate, modestly unpleasant feedback every single time you pressure the heel. And your calf muscles will cramp very quickly if you try to hold your heels up without getting forward.
Just don't keep the pebbles in long enough to bruise and don't put anything in there big enough or pointy enough to damage you if you have to throw on the brakes.
I haven't tried this yet, but I have certainly thought about it, and if I can't get my new found skills of staying forward on moderate slopes to carry over to the steeps, I do plan to employ this technique. (But then, I'm just a teensy fanatical.)