@supersook - There are a few tools that can do this. I would recommend a router with a flush trim bit.
Pull the acrylic out and very carefully lay it along the edge of a scrap piece of wood (a sheet of something would be ideal). The amount you want to remove from the acrylic should overhand the support sheet. Clamp it down good & hard.
Set the depth so that the bearing rides along the support sheet and the bit trims the acrylic. Go fairly briskly as acrylic likes quick cuts. Slow cuts will have the bit rub against the acrylic and melt it. You may wish to practice on scrap a couple times first.
