You don't want to meter through the filter, and also catch the effect of the filter.
The filter is used to block light. Selectively.
If you don't want the parts that get darker as a result to get darker, don't use that filter.

So only use the fixed filter factor of the polarizer. The one that compensates for the overall, non-selective blocking of light.
So no TTL, through-the-filter metering to include the effect of the filter. If you think that the polarizer makes things look too dark, ask yourself: why are you using that filter?