Restoring files from interrupted TIB backup set

I'm pretty sure that I've got no hope on this one, but I thought that I'd try the forum, just in case.

I have a friend that has been using TIH 2009 for a while. He recently bought a 2TB external USB drive and played around with backup schedules. The external drive is a FAT32 format, so when the backup occurred, it backed up the entire PC (around 700Gb), but split it up over 181 4Gb files, taking about 15 hours to backup. Unfortunately, a second schedule started another full backup shortly after the first one finished. He cancelled the second backup shortly after it started, but it rendered the backup set no good, getting the "This is not the last volume of the backup archive." error message whenever attempting to mount the backup.

He now needs to recover some files from the corrupted backup set. Because of the fact that the required data was on the third volume being backed up, I'm sure that the data still exists somewhere in the last 40 backup TIB files, which were not overwritten by the second backup job. I've searched through the files (using hex edit and similar), but cannot find the files, presumably because the backup zips the files or similar.

Is there any tool for being able to recover files from a backup set where it's been interrupted? Do I tell him that his files are gone for good?

Thanks.