scheduling backup 'when backup volume is available'

[ChrisRyland]

I wonder if the following would be a feature that others would find useful.

I've set up my daughter's G4 PB to backup nightly at 3am to a 1GB USB flash drive. The problem is that machine is usually off at night (she's pretty mobile, and thus it's never really sitting on a desk), so backups won't happen much of the time.

What would be ideal if there were some way to mark a given script to run at a given time, but falling back to 'when backup volume is available', leaving SD running all the time in the background. Then, when she inserts the flash drive at whatever time she remembers to do it, the backup would start right away. (Is there some API for SD to be notified when volumes mount? I suppose busy-checking once a minute would be good enough.)

Thanks.