I think you are missing some magical powers... Just kidding, there is a way.
In the Where Used tab the option to show configs may be greyed out. If you have it on All Versions you can't pick a config. So pick a version (of the child part) and then a config, and then it will show only the assemblies where that config is used (and the name of each assembly config that uses it).
So you can have an assembly show up more than once if various sldasm configs use your part (with specified config).
A small related tip: You don't have to actually open the assembly file, the EPDM BOM tab for an assembly most likely shows a Configuration column. (If you don't see the config column you can add it to the "BIll of Materials" section of the admin tool. )
Thank you so much. This is exactly what I needed. Thx.
The problem with this method is if you have 17 version of a file you have to look at each version. I suppose you could export each out and combine them. Am I missing something??? I want to do a simple find all parents where a configuration of a model is used in.