I'm trying to book a combined ticket EWR-PHX on CO, TUS-LAX-JFK on UA. The CO portion cannot be booked separately as it's not available as a one-way fare. I would like to upgrade both legs, the CO flights using CO miles and the UA flights using UA CR1's. Is this possible? Once ticketed on CO, can I go to UA and have them change only the UA flights to my MP number and request the upgrade?