Just authorize the MBA with both AppleIDs and that should solve all of your syncing problems. You can authorize more than one AppleID to a single computer.
No you can't. It's actually the opposite. You can authorize multiple computers with a single Apple ID not multiple Apple IDs on a single computer. These may sound the same but they are very different.
I have two Apple IDs each with some previous iTunes purchases associated with them. I recently decided to try and get my old content by logging into the old Apple ID. During the process I was asked if I wanted to bind or attach this other Apple ID (don't really remember what it said) and thought fine, do it.
Well, later on when I wanted to go back to using my current Apple ID I got a message that read "This computer is already associated with an Apple ID. You can only download past purchases on this computer with just one Apple ID every 90 days. This computer can be used with a different Apple ID in 90 days." Now I am locked out of downloading purchases on my current Apple ID for another 75 days! AppleCare didn't have any help here either.
WTG Apple! All this unneccessary aggravation could have been avoided if you just allowed us to migrate or merge Apple IDs. I certainly hope that there's some truth to you fixing this issue.