Originally Posted by qasr
Short answer: no.
Long answer: Only at booking time or check in time. Since you can only check in for domestic flights, that means international flights only have the one option. You'll have to call UA.
I was able to get online checkin for SEA-NRT last week!! It was a UA.com file with the first leg on Air Canada and I used AC.com to get the boarding passes. Does that make a difference?