This is what I did:
I was planning to buy a PE "E" class ticket. I found out just in time that "E" class is not easily upgraded (lots of fees to equalize the fares, etc).
I bought an "S" class ticket in PE - only marginally more expensive for 3 - a few hundred dollars difference THEN I upgraded to UC as "G" class fares were available for 90,000 points (I've been saving a while). "S" coded fares are eleigble for upgrades.
Now, if you haven't saved this is perfect timing! If you're planning for two people flying, you can purchase 30,000 miles for $800 or so BEFORE Dec 31, then buy 30,000 more Jan 1. From what I can tell, it would cost $1500 or so to upgrade 1 fare from PE to UC, so you save approximately $1000. At least that is how it worked for me (SFO-LHR).
Then you have to call UC reservations through FC pretty much every day until upgradeable seats in UC are released and you can snatch them up. I found a great little tool that I could check myself everyday to see when they were available. I had outgoing booked a month before return was available. I knew the upgrades were available before the UC FC person knew!
Happy Hunting!