Displaying related custom content types

I have created a module for Products and another for Promotions.  A particular product can have multiple promotions going for it at the same time.  I can setup product promotions as a related data field.  This all works good and I can add all the promotions to my product.  I am now not sure how to control the display of the product / promotion combination.  When I drop the product content widget in a page, I can select the individual product but how do I select/filter for a particular promotion / related item?  Even if i could set a parameter (like promotion name) that the content widget does filtering on in the template would work, but not sure how to pass that in to the product widget.

Ps: We use feather on 9.1.

PPs: i have already seen this example docs.sitefinity.com/example-filter-dynamic-content-items-by-dynamic-field however I am not sure how I can give this functionality to the marketing person dropping the widget on the page.  How can this example be extended to allow the content widget to be customized once it is drag and dropped to the page?

PPPs: Also have seen this docs.sitefinity.com/feather-filter-dynamic-content-items-by-related-data, but it doesn't allow the person dragging the content widget to set the filter.  I.e. in step 7 I'd want to show only certain cities not all to begin with. 

PPPPs: This docs.sitefinity.com/example-query-dynamic-content-by-related-data article is basically exactly what I want to do. Except the filter criteria ("Neurology") can't be hard coded. Needs to come from when the custom content widget is placed on the page.  Is there a way to pass parameter(s) to the custom content widget template?

I ended up going the route of a custom widget.  With its designer I can add whatever parameters I want to filter/select by.