I'm doing a lot of flying from CLT to Hong Kong lately. Since US has no options on this route I'm doing a United flight out of Chicago. My client mandates Y class and as a big guy the extra room of FC would be nice.

I've been booking through UA's website since pricing is significantly better than the US codeshare price, but I'd like to use my US miles to upgrade to FC. Is this possible or would I have to convert miles in another program to a United account and go that way?

I've been tempted to switch to UA's program, but being a CLT resident means I'm sorta stuck with US.