Using a CREO trail file is probably the easiest method to achieve success.
You would begin with a clear cache, define your backup directory, then
go through all your steps: 1. "open in CREO" 2. File -> Backup 3. Close File, Erase Not-displayed and Close CREO
You can then take the trail.txt file, and modify it for each assembly file, and run them one at a time or string a few assemblies together.
You'll have to be careful on how much data you can process for each session, because you could exhaust your allocated cache space.