Reference:
Calumet Rosco Polarizing Filter (part #RC3000) mentioned in a previous answer to a gel polarizing filter question.

My experience with glass polarizing filters, when many years ago I used a 35mm camera, this required rotation of the polarizer to the correct incident angle to the sun or reflection in order to get the desired effect (e.g., darkening of blue sky or reducing/eliminating reflection of water). Gel filer polarizers sound like the solution for LF - but, what arrangements have you experienced LFers made to accomodate such a polarizer for use of a GEL polarizer on your LF cameras (i.e., rotation)?
It seems to me that just placing a gel polarizor in front of a LF lens without rotating it to the correct incident angle will be just a blind exercise/guess unless you could look at the ground glass on the back as you rotate it. Then there is the problem of what kind of filter holder will accomodate this?

Any advice would be appreciated.