In order of recommendation:
1. Assuming you can rent it (e.g. not an exchange with II), I'd go with that option first. Trying to swap with an owner is not easy -- TUG has a place for that but not sure if I would go that route. Trades appear to be rare.
2. As someone else pointed out, you can drive to Palisades which is included on Ikon though I would not advise that. With Christmas crowds, I think you are looking at long lines and well over an hour commute time (say two or three) one-way. You are probably better off buying a 4-day Epic Pass or something like that to cover your needs and ski at Heavenly, especially if staying at the Ridge which has the gondola that drops you off right at Stagecoach.
3. Last resort would be to bank on a trade/swap. Trading via II might be possible if you are looking for accommodations similar to The Ridge level tier but Christmas ski week as you know is tough. Trading with another owner would be tough as mentioned above.
You must have a good reason for buying Ikon, but I was curious why given the above request plus where you live and the timeshares you own. It screams Epic Pass. Not judging -- just curious. I can see getting bored of skiing Heavenly every year
Good luck.
-ryan
