Using an import mapping parameter to find existing mendix object

original question: https://community.mendix.com/link/questions/91148

I am trying to use a parameter in an import mapping. I can use it to set as a parent object, but I also need to be able to set it as a microflow argument to lookup an existing mendix object (as I need a composite key of operating company and registration number and I can only set direct attributes as keys), see screenshot.

So far I worked around by copying web service results in non-persistent entities first and then manually find existing items and then simply copy all attributes in a custom microflow. However this seems to slow things down with huge datasets (even leading to out of memory errors).

Could you add the possibility to set the parameter in the lookup microflow or allow also associations to be selected as a key?