Transaction log truncation with sharepoint (2007) backups

Hi folks
Im testing backup of my sharepoint (MOSS2007) environment with netbackup 6.5.4.
The backups are running nicely, we have still to test the restore part.

My problem is that our sharepoint production databases are mirrored, hence running in full recovery model.
Anyone want to share experiences handling transaction log truncation with an installation like this?
- from what I can see, there are no built-in agent features to handle it?

thanks