has released AutoStart PRX, a 3.90 M33 compatible Custom Firmware plug-in that, as the name implies, allows users to specify a list of up to four separate homebrew applications to load at launch.
Each application can be binded to certain keys. When that key is held during bootup, the PSP will automatically load your homebrew. As always, refer to the included readme file for installation and usage instructions.
Download: AutoStart PRX Plug-In for M33 CFW for PSP
To quote: Here's a small plug-in I've made that allows you to launch your homebrew at startup. You can configure it to launch up to four different eboots with the included configurator.
For example, by holding cross at start up, you can load one homebrew, while holding triangle will load another. Hope you like it!