I use the knee pin quite a bit and shut down my gym's best triangle guy. I learned it a couple years back from a traveling black belt. His variation has you hug the knee, pin on the floor, and then get off your knees and into a Hindu push up. The Hindu push up generates tremendous shoulder pressure breaking your partners figure four. Depending on how my partner let's me grab I then pass the guard in either direction, I prefer knee sliding over the already pinned leg.