1. There's no way you can pay the one way upgrade fee in advance and get this confirmed. Period.
These upgrades are for sale at check in only, if available.
2. You can on tickets bought here in the US (and some other markets), change for a fee and get seats confirmed in advance. You then have to pay the change fee (2-300 USD) AND the fare difference (probably 3-4000 USD at least).
I didn't know they had jacked the upgrade at check in prices up that much. A 80% price increase is crazy in my book...

(I thought only UA had the guts to make this kind of price increase)
Can anyone confirm if these prices are current?