This could possibly work for you. I have made some graduated filters from Cokin or Lee clear (I believe) polycarbonate square filters by dyeing them in RIT fabric dyes. The dye solution was very hot and they did not warp. They can be cut to size but I don't know about the color wave length. The optical properties if that is an issue are very good. But I think they are more than 1mm thick. Also check Anchor Optic division of Edmonds Optics.

http://www.jeffreyglasser.com/