This was just released seconds ago:
Yoshihiro, of WAB, has released a PSP Version Changer:
What this program does, is trick games that require firmware version 1.52 to run on your 1.50 PSP.
The implications are huge. You won't have to run the updates that are required by new UMD games, simply load this EBOOT, and it makes the system run the game anyways.
As an extra benefit, if you try to run the 1.52 updater on your 1.5 PSP using this EBOOT, it won't update. Think of it as a sort of 1.5 firmware update protector. No more accidently flashing your firmware.
From the .nfo file:
Yoshihiro and WAB are proud to bring you The First Firmware Trickz for Gamez that need Firmware 1.52 to run on your PSP and Cant Run UPDATER 1.52. The System think it's a PSP v1.52 even if its a v1.5.
Good job Yoshihiro and WAB. Keep up the good work!
Download this file here
Forum Topic here