When we are doing variation data for matrix items you are asked to populate producttype/TYPE/VariationData/Parentage
Where all your products in the relevant store are matrix items you simply insert the word child into the override. Where you have mixed matrix and non-matrix items you need something cleverer:
Set up a field mapping in NScSync to push the following mapping to a webstore field (marketplace_text#, where # is between 1-20 – the number of currently available marketplace text fields, used to supplement your data for Amazon):
case when ISNULL((select TOP 1 ItemClassID from itemclasscomponent inner join itemclass on itemclass.id=itemclassid where itemid=item.id and classtype=0),-Item.ID ) > 0 then 'child' else '' end
Then map this field to the Parentage of the product feed. It will populate the field in the product feed appropriately with either child or an empty string.