stoker25 has released a great app for your jailbroken PS3 console where you can redirect dev_flash and app_home to your USB. Not sure what can you do with it as i am not a developer myself but you can always check below the release note from stoker25 himself. Oh ya, to be sure with it, you cannot load full CFW since LV2 is still in the memory.
It’s a clone of JaicraB’s USB FIRM LOADER, with a few differences for people like me with USBs that have different numbers
->Choose what USB to use!
Redirect dev_flash to usb
Redirect app_home to usb
Dump LV2 kernel and mount points
…along with all the source code that does it
!!!NOTE!!!: You need a payload with peek and poke syscalls (PL3 dev has this)
X – (Un)Patch /dev_flash as usb
Square – (Un)Patch /app_home as usb
Select – Dump lv2.bin & mounts.bin to usb
Up/Down – Change USB
Triangle – Exit
The dev_flash files have to be on the root of the USB drive to work, e.g. if E: is your drive, you should have E:vsh, E:vshmodules, etc…
Make a PS3_GAME folder on your USB for the thing in the Game menu to work.
App has some bugs, but it is my first PS3 program
JaicraB – original CFW loader
dwarfcrank – reversing the CFW loader