Post Grid: filterable by sub-categories?

Hi everyone,
I have a category that has many sub ones. What I'd like to be able to do is to tell the grid to show all posts attached to the main category by simply selecting the main category in the query, but while having the possibility to make it filterable by sub-categories for the user. The only way I can do that right now is by selecting all sub categories in "query post" instead.
Thanks for the help. Your plugin is awesome.