I tried the oven method before finding this article.
This method was used on 1980's era playfield plastics.

I used two small sheets of plywood and a micro-fiber cloth.
Preheat the oven to 250*F
Sandwich the plastic between the two pieces of plywood - wrapped in the cloth to prevent transfer of wood-grain onto the plastic surface.
Apply metal c-clamps for even pressure.
Allow to heat for 15 minutes.
Remove from oven and allow to cool completely while under pressure.

I went a bit over and heated my first plastic for 25 minutes.
The micro-fiber cloth began to "etch" the plastic so be cautious. This can be buffed out so I didn't really make a big mistake.
250*F for 15 minutes is plenty of heat without offering too much danger of ruining plastics