Hehe, right, i missed that 20 and it explains the 176. Apparently you cannot use negative numbers regarding PP.
Ok, i have a final effort.
You know that timing method '9'.
I call it permanent after death, but others call it permanent after bonuses.
My further research seems to prove those others are 'right'.
The 9 timing method is used internally for delayed effects that have been fired, so they don't supposed to be expired.
So, if the 'after bonuses' part is true, then you could add a set PP to 0 effect with timing method 9.
It will remove that 20, hopefully
Just make sure you use 'set' and not 'add' and the timing method is 9!