Just set the all metal switch to PP mode and not the All Metal track or fixed modes. Now flipping your other switch from Disc Iron Mask ON (that most people use) to All Metal will then turn control over to whichever mode you have the other switch set at (in this case PP mode).
If you scroll down the threads in the last few weeks you'll see a few threads on PP. Some guys report PI depth and ability to cut through bad minerals with it, and one guy listed a bunch of PIs he's owned that he said PP mode is just as deep if not deeper than. That was impressive to read.
Use PP mode when mineralization is super bad even for BBS in disc, or when targets are so deep that they are even out of reach of disc. Volume at full for more depth in PP and you can run sensitivity all the way up too compared to what disc can use. I'm still new to PP mode but I can often already tell if it's iron by the fuzzy approach/leaving of the target or by one way sound offs, without even needing to flip to disc to double check. I hear there are at least 10 distinct words to PP to judge targets by, which puts it at PI depth with disc-like discrimination abilities.
Here's a video/pictorial I did on disc vs PP mode on the GT. A few days back I updated the content of this video as well...
http://youtu.be/G817__EOC8A
You can also find another "video" (which it ain't) update on PP mode at another mineralized beach on my channel. I'm planning more videos of PP to show how it hits at targets only 4 or 5" deep at a badly mineralized beach where disc is choking out due to the really bad sand. Plan to also show the target response that indicates obvious iron hits in a few ways.