With a Pyrex measuring cup, a little water, a piece of PVC, and a microwave you can shape plastic pieces that enable you to do and make useful things.
WARNING: Our PYREX cups are several decades old and work well with high heat. I just learned PYREX was sold to a company off-shore that uses a different composition for the glass, and it is prone to exploding violently under heat stresses that were no problem for the original PYREX. It sometimes explodes as you are removing it from an oven. (October 12, 2009)
Step 1: From round to flat
Pictured is a half-round piece of PVC I had left over from another project. The flat square was made by cutting a piece from the half-round and heating it while the water in the Pyrex cup boiled in the microwave for two to three minutes. I removed the cup from the microwave and used the tongs to pull the PVC piece from the very hot water. The tongs also helped to unroll the softened PVC so I could place the piece of wood over it and hold it flat against the countertop until cooled and firm. In the absence of a good supply of Plexiglass, some PVC flattened with the aid of a microwave and some hot water offers some impromptu versatility.