ok i wasnt completely accurate... i do not mean all the songs he will ever write.
it comes down to the rules on "collections". it is not cut and dried and there are varying conditions for previously published versus unpublished... you can even pre-register i believe. Dont take my word for it.. check it out yourself.
colections are really intended for say an album of songs or literary works published together in a book but if you have multiple works of any kind you can collect them together into a collection and submit them under the title of the collection incurring only one submission fee.
as mentioned there are criteria to be satisfied. you need to check these yourself until you are satisfied.
in this case, for multiple unpublished works that seems like a good idea. if it is a mix of published and unpublished works then true more than one application will be needed.
in an ongoing basis this could be maintained at an album level for example.
if you have an album of songs you use the online submission form and enter a title for the collection (the album title) follow the instructions (dependent on what you are submitting) and submit.