Ran across this: http://erwin1.blog64.fc2.com/blog-entry-25.html
Google Translate: http://translate.google.com/translate?sl=j...tml&act=url

Perform at your own risk. If I am reading this correctly, if you cut the PCB along the red line, Down will no longer be held. You can wire a switch to join GND to the cut-off part so that you have Down held while used on PS2, and not held while used on PC.