Circ Polarizers and Sigma 15-30?

I've almost talked myself into the 16-35 for the extra speed and full-time manual focus override, and that I keep reading "filter incompatibility" for the Sigma offering. I know it takes rear filters -- which makes me a little nervous about the frontal element hiking in the mountains and taking photos in the wind -- but how does this work with a C-PL? Is this another reason I should get the Canon?

The best case I can think of is that you would hold the filter to your eye and rotate it, then put it into the lens that way ... but I'm not sure this would work?

Can anyone enlighten me?