"you lost me at switcher"
that probably means this isn't the type of project for you.
Let me know if you want the big instructions i'll be happy to help. Basically I'm suggesting you analyze the M/B enough to find out which is the AGP power supply and remove one of the components. It might not be that hard for somebody with some skills in electronics (board level).
It would most likely still be possible if it were a switcher, but even more electronics intensive. Maybe even impossible without at least an oscilloscope.
At the end of the day if you make bad choices during a project like this, you can kiss major computer components bye bye. The rewards however might be fun.
PS you should know that I have no idea what the ramifications of actually pulling this off would be. ie how much of a bump is safe? and what will it gain you?