enable top 5 volt w/ serial gps

Hello
I was wondering if anybody knows of a prx to enable/disable the 5 volt source on the top of the psp beside the usb port. If you're using the GPS-290 with mapthis (ENABLESERIALPORT=0), it turns on as soon as you load a map. But with ENABLESERIALPORT=1 it doesn't turn on at all...makes sense, as you don't need to power the GPS-290.

Reason being, I just picked up a serial gps unit (http://www.ytec.com.tw/Modules(GPS)/...DS-ENG-1.0.pdf), but I need to supply it with 3.3-5 volts and I figure the top of the psp would be a easy spot to get this. I suppose I could tap the battery terminals too...
Anyone have any suggestions?