I've been working on this for some time now, but after lots of testing it's finally complete:
PSP Installer 1.0
It's a homebrew application that let's you make your own PSP EBOOT.PBP self-extracting installer! (no compression)
To use simply put the EBOOT.PBP and the installer.conf (the script to run) in your game's PSPInstaller directory and run it. This will create an ARCHIVE.PBP which is your installer.
When you run your ARCHIVE.PBP (EBOOT.PBP of the installer), it will extract the installer.conf in your application directory and starts executing the script (the installer).
Comments about how to write the installer.conf script (MUST be written using windows/dos CRLF) are in the given installer.conf file.
EDIT: Reuploaded the application because i've forgotten to remove a row of code that made the software think you always press CROSS. (to test it in JPCSP, i had to remove all input with this to test it)
EDIT: Removed the file for now, because it crashes your psp when run on the psp..... checking it now...