Reaver from TeknoGods has created a simple application that converts your PS3 ISO’s to PSJailbreak format, allowing it to be ran with backup manager.
To quote from readme:
1. Run tool
2. Open your backup .iso
3. Make folder called GAMEZ in your external USB HDD
4. Extract ISO in GAMEZ (do not make any subfolders!)
5. Run Backup Manager on PS3 with USB HDD plugged in
Required: Jailbreaked PS3 with backups enabled, External USB HDD
This release is beta quality. If something breaks, review any
pertinent comments on teknogods.com, then email me as a last resort.
Include all log files and a detailed description of problem and
how to reproduce it.
Thanks to sonicjam for the tip.