No, I don't think you can make a generator. When you remove the dielectric, the amount of free charge (i.e. the charge actually on the metal plates) stays the same. The total energy of the plates+dielectric system also stays the same.
The plate potential goes up because the dielectric is now depolarized and has no electrostatic energy anymore. This energy has been transferred to the capacitor in the form of increased potential. You could drain off some "extra" charge to reduce the potential back to the initial value, but when you put the dielectric in again it will repolarize and reduce the potential even further.
Putting the dielectric back in is the reverse process. The total energy does not change. It requires no force to put the dielectric back in. Therefore there is no work done.
EDIT: LOL ok apparently you CAN. That Wimshurst machine thing is cool. I imagine that the asymmetry is key to producing forces.