Adding another step to your backup job to perform the move might work as well. If I have it right:

 - You're creating t-log backups every 11 minutes [11? 10, 12, and 15 are all even factors of 60 minutes, why 11?]

 - All backups that occur within a given hour are loaded into the same physical file

 - When you get to the "next" hour, a new file is created

If so, having a step 2 that moves (or copies and then deletes) all files "prior" to the current file to your destination should work. Your current backup file (set) isn't touched, and your old files are deleted after their copied [but be darn sure the copy is succesful before deleting it!] If the file's in use, the copy or the delete will fail... only to be processed again with the next run.

   Philip