Go into Autostart plugin, select a button to hold down for activating your PMF (I found that the actual autostart without selecting a button doesn't work). I like to use L trigger - and I probably wouldn't use R trigger as that may fudge something up in regards to getting into recovery menu.

Don't know how it may differ for you on your firmware though, I'm on 5.00 M33-6 (with faster memstick reading on ALWAYS)