Dynamic Contact Group filtered by Items Purchased

I am trying to create a dynamic group of contacts to be used for a marketing campaign. I want only the contacts associated with customers that have purchased items that have a particular value in a custom field that resides on the item record as well as on the invoice column.

Using a native NS search is not working for me; I find I need to either list all customers or list all items, not filter the item based on the custom field value -- a very manual approach.

Can someone tell me what I need to do? Thanks for any thoughts or tips.