This idea may have been thought of and may not work. If there really is no version check on this update, then this may be possible. You will need three memory sticks(or a pc with a memory stick reader. I am specualting, and have not tried this, so i am not responsible if it does work for any bricked psps. You will need a bootable eboot such as the first part of WABS beta downgrader. After that when the screen starts to fade to black, press the power switch three times to go into stnadby, and switch to a second stick, which will have the dummy update. if this loads, press start, to see the details and then swap the stick to a 1.50 update stick. Try and complete the process. This may be way off, idk, but this has been untested, so i can not say. SOrry, if this has already been thought of.