Help Me Auto-Eject Disk After Backup

[Alameda]

I have an external USB drive that I use for Time Machine backups. But I use it in my office, and the problem is that I plug it in, do a bunch of work, and then I suddenly need to dash off to a meeting, and it takes quite a while to eject the USB drive, especially if my MacBook Air is asleep.

I'd like to get Time Machine (or a different backup program; I don't really care) to run a backup and then eject the removable USB drive. Can someone tell me how to do this?

Thanks in advance!