I'm sure there is a better way to do this, but this will work for you.
Create a new table that looks like your csv file. Then import into that table. Now do an insert in your ID'd table selecting your values from your new table. Finally delete everything from your new table and keep it around for when you need to do this again.
INSERT INTO id_table (col1,col2,col3, ID) VALUES
SELECT col1,col2,col3,NULL FROM new_table;
Or something like that should do the trick.