Best way is to file an issue on github to add the association: https://github.com/Erwin-t-Hoen/Flat-File-Importer
In the past i have retrieved the created objects by means of ‘createddate’ or by adding a new temporary object. With the last one you delete the temporary objects when your process is done, that way you can retrieve the complete list every time.
Both are not pretty options though.