The frames on the P are not projected, as they are on a 7 or Leica M. (If they were, blocking off the 35mm finder mask would work exactly as you describe, although it would be a touchy job.)
Instead, the P uses reflected framelines. If you hold the camera at reading distance and look into the eyepiece from the rear, you'll see that they are actually silver lines etched onto a flat glass plate just inside the eyepiece. This plate is somewhat delicate, and would take a very light touch to remove. Once removed, though, you could start thinking about what to do about the framelines.
Taping or masking over the 35mm lines on this plate (on the side away from the eyepiece -- that's where they reflect) would eliminate the 35mm frame, all right -- but at the expense of masking down the entire eyepiece, most likely making it more difficult to see through.
If you didn't mind the risk of ruining a perfectly good P with the experiment, I suppose you could eliminate the 35mm lines by scraping them off... or, better yet (IMO) you might be able to subdue them by carefully lining over them with a fine-point felt pen.
However, if you're going to go to the trouble of taking your P's finder apart, I think you might look for an alternative. It could be that the reason you find the 35mm frame "blinding" is that your camera's finder optics have hazed over a bit, smearing the 35mm frameline image and making it more of a distraction. A careful cleaning of all the outer optical surfaces might improve this enough that the 35mm frameline no longer would bother you.
