Gelatin filters - How to attach?

I have some gelatin filters (Wratten 89B) that I cut and attached to the lens using tape
However I was thinking there may be an easier way using the Cokin system.

Any ideas on how to make one for it? Cardboard? how thick?
Filter are 75mm square so they'll fit the cokin system A real well.

Cokin makes gel frames that hold the gel and slide in like resin filters.

I have a clip-on gel holder made by Voss that cost something like $15 used from KEH. It has two barndoors to shade the lens and fits all my odd-sized lenses up to around 77mm.