Today THANKS to a find by Vampire we now have UMD RUN v1.0 for the PSP! To use UMD RUN v1.0 with your PSP v1.50 firmware, simply install it using KXploit v1.50 and then (with a PSP UMD Game Disc inserted) press X at the PSP Menu screen to run it loading the Game's BOOT.BIN via UMD on your PSP console.

Before people ask, this current version will NOT run UMD image dumps from a Memory Stick, however, RUMOR has it to load executables from MS on a PSP v1.50 you'll need to set the kernel mode flag in module info and run sceKernelLoadExec from a thread with flags 0x0000 (0x8000 doesn't work) so only time will tell what the future holds. Cool discovery though!