Use a pathfinder awl or blunt needles. I have a Triad 3 to string with Power Holes. I doubt a pathfinder awl will fit but I think a small blunt needle will.
EDIT: My guess is the Power Holes you are talking about are the ones on the older rackets that did not protrude through the frame which is a bit different than the Triad 3 but same principle. First push the needle through the Power Hole from the outside and place the tip on your finger to steady it. With a point cut on the string place the tip of the string in the needle and push the needle out.
A desk lamp or a flashlight helps me to see the holes. Prince also has a variation on this grommet system fro some of their older model frames. What works best for me is good lighting and a string that is not black.