ONLY for fw 3.03 (by now, in the future it will also be possible for more advanced fw's)
Copy the contents of MS_ROOT inside your Memory Stick Root and execute the flashbackup from Games-Memory Stick, and follow the instructions to make a flash0 backup, dummy your jpn0.pgf file and/or execute directly the flasher.
- Caution! -
Don't delete the _SCE_1 folder inside of GAME150 (shows on the XMB as corrupted data), as it's the base of the XMB work.
Disclaimer of Responsability:
The author(s) deny all responsability concerning to problems with your PSP flashing proccess; it's your responsibility to decide to flash this app into your PSP. This has been tested, and it works without a problem if you follow the instructions upwards explained.