I often use the ticket desk (far left desk at elite check in for UA intl) at Intl for doing this - easier to park in the intl garage and there is generally no line after the mid afternoon departures to Asia/Europe. Not sure if they care if the ticket is intl or domestic (I've always done Intl) AND you can grab an emporio rulli coffee or go all out at Ebisu and spend $20 for free parking. Only one ticket agent there though.