We have just received word that homebrew developer Dark AleX has recently finished work on a new project, dubbed the PSP Mac Spoofer. This application temporarily changes the Mac address that your PSP sends to WiFi Access Points and similar WiFi devices. Quoting Dark AleX's readme for further clarification:

This plugin does NOT:

• Change the mac address stored in idstorage (that's useless, as that is just to show the inf in xmb). Therefore you will still see your old mac in system info.
• Change the read only mac address stored in the wlan chip.

• Change the mac address that your psp will send to other wireless devices. This is useful if you want to hide your real mac address to other people for some reason, or if you want to bypass some mac filter protection of your neighbor :)