I'm thinking that i might be able to glue a step up ring on to the housing as just screw on the filter when i want it.
I bought a 37-43mm step up ring and a 43mm filter, but i got a pretty big vignette
with just the step up ring

ring and filter

so i'm going to return those guys for a 39-52mm
i think the 52 will look pretty goofy on the gopro, but it might just work
has anyone else tried to put a polarizer on their gopro?