Other idea, as unexpensive solution for DIY's: to use the plastic polarizer usually found in most LCD-equipped devices; a broken or obsolete cell-phone could serve for this purpose.
It is a plastic light-grey material, glued with a contact adhesive at back and front of the glass surface.
[img=left]http://www.polarizingfilm.com/prodimages/polarizer-P210-large.jpg[/img]
Can be taken apart starting at one of the corners with a sharp tools like a knife, and the can be ripped off easily.
[img=left]http://lh6.ggpht.com/_kunDbqDzBNg/STqducsaitI/AAAAAAAAAVw/qMjVJeZk_3g/a1.jpg[/img]
The remaining stains of adhesive can be removed using domestic alcohol.
This material could be easily cut with scissors, in order to get a disc adequately sized for our particular lens.