I've seen a few different ways people handle this. Here's how we do it. Example:

Player is searching for a clue. It's a <P> roll for the superficial clues, but a <PPPP> for the hidden clue.

I have the players make a standard <P> roll, and I roll the other <PPP> behind the screen. I do this on any roll where the outcome may be hidden from the player. It also allows me to just 'drop some dice' (even if it's a simple <P> roll) so they aren't sure of the difficulty.

It's worked out very well for us.