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.
I have a little shake in my hands now so I generally place a finger on the racket and grommet to help guide the string in the grommet. I do the same for the needle on Power Holes I can't see.
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.
Don't get discouraged. The more you string them, the easier it gets. Soon, they will be just like any other hole. Keep the tip of your string cut at an angle to make a point. That helps too.
Better lighting condition will also help alot,,
im almost to the point of frustration with my room lights that I might wear thoes headlamps when stringing,,, haaa