I use a shitty UV filter on mine most times, not being built well, it's thick and sits off the lens a bit. If you bought a quality CPL that was thinner and didn't sit too far off the lens you would probably be fine, I can't remember ever seeing vignette.
Can I see an example? And Twoods (tyler? trevor?) How thick is the UV? I have a 77mm B+W CPL that vignettes on the 12-24, and the difference between the lens is about the cost of a new CPL so I may just swap lenses instead of buying another. Plus Ive been slowly looking at the 11-16 since I hate slow lenses.
"any one have a brazzers account i can use for like 20 mins?"
The brand is Sunpack (from best buy) My UV filter is a hair over 5mm tall, the CPL is 8. I cut an 8mm thick strip of tape and taped it around the edge of the UV, you for sure get vignetting at 11. Goes away by 13mm.
I suppose if you can find a sub 5mm tall CPL it would work, but I'm not sure where you will find that.