Best way: Don't shoot into perspex.
Second best way: Get your lens right up against the plexiglass so that it blocks out any light that could cause a reflection.
Polarizer isn't really a good technique for this situation. It cuts out some reflection, yeah, but it won't get rid of all of it. Also, if plexiglass is anything like the glass they use in airplane windows, not only won't it cut out reflection, it'll spray rainbows all over your shot like a bukake video set in a magical kingdom.