Question Is it possible to tap into Yoast Primary Category when showing related posts?

[maryannstoll]

I have posts that are marked with multiple categories. Yoast sets a "primary" category that of course, the author can change to be any of the selected. I'm familiar with using the post query = related >tags>category setting. Is there any way to either use a different widget or to hack this one s.t. the filter/select criteria is restricted to the "primary" category instead of all of the marked categories?

I want to do this when showing related posts AND when listing the post meta=categories.