Populating foreign key fields when importing from excel.

I want to populate a table from an excel spreadsheet, a child table to my master projects table in my fm db. The foreign key field I need to fill is the "project_number" key, since I am using an internally assigned fm serial key for each respective project number assigned by the user. 

So my thinking is. Populate the projects table first, have fm assign a pk for each project, then somehow find a way to relate fm assigned serial to existing project no. in the spreadsheet and then import it? Surely there should be some easier way...

(this of course stems from the fact that I 've opted for an fm assigned pk serial, instead of replicating the XXX-YY (X:number, Y:year) project no we currently use, and using that as an fm assigned pk, after having inputted the data already available. Maybe I might need to rethink this. I hope I can input the project no.s in a field and then, from then on, have fm assign itself the XXX-YY code, that is change the type of field to autoenter without affecting the previous records.)