I'm in the same boat. I have a Dimension P3-733. The molex has eight sets of pins that go to the MB. I can trace four (4) back to the power-on switch.
I thought about soldering wires to the backside of the printed circuit board that holds the existing switch, bu my soldering skills aren't that great.
Then I read about splicing the wires, but I'd have to strip them first, and they're all kinda small and bound together in that stupid ribbon cable...
Then I read about randomly shorting out the pins on the MB to see which ones turn on the computer. It seems like that could hurt something, though? Anyway, if you found those, THEN what would you do? Jam extra wires up inside the existing molex and force it on?