What would you like to do with the list as the formatting MF is used to format the data in a single attribute.
It sounds like you want to create an associated list of ID’s for the records based on the incoming list of ID’s in a single attribute. If that is the case create an entity with an integer attribute and create an association between the original import table and the new one. Then make sure to split the ID’s into integers and create the records in the new table and associate the new record with the import record.
This can be done by means of post processing the data and maybe during the formatting.