Do you know how to create scripts?
Do you know how to work with a $Path variable to refer to different files by differen names and paths?
If you place your folder of Mp3 files inside your Documents folder, FileMaker can extract a list of all the file paths to the mp3 files using get ( DirectorypathListing). It can then loop through that list, importing each detected mp3 file to insert each one into a container field. You can then use Export field contents to export the iinserted "by reference" files to a location where you want to store the files. After exporting the files you re-insert them to update the file reference stored in the container field.
Obviously not a simple option, but one that can be made to work.
This thread on $Path variables that comes with a tutorial database file on the subject may be helpful: Exploring the use of a $Path Variable in Scripts