Right now you can use Stygan spikes or Siphon MP for this purpose. But i believe that once jobs are added, since they will restrict the cross-class actions usage, some kind of MP regen might be added to PGL.

But indeed i'd like having different costs/penalties here...maybe changing it to HP penalty instead of MP...if instead of 10 and 20 MP it was 20 and 40 HP it would be much better for PGL.