It seems to me a rotto zip would work if it didn't create meltdown then an the idea of an old iron bed rail used to C-clamp the plexi to a table or piece of wood then with a small 1/4 inch collet wood router
using a fairly thin but not too thin flat ended spade bit might give a decent and clean cut by slightly lowering the blade with multipul passes
of the router to avoid meltdown by taking less material and moving the router a little faster
this way CAUTION I wouldnt cut all the way throught using this method it may shatter.
I will cut just over half or two thirds of the way
through then score and bend it.
I am going to try something similar to this idea
that I came up with while I was here at this Site.
Thanks for stirring my thoughts......Ed