I don't think writing him something is a cop out. I mean, it's personal and one of a kind. I think a song would be an intimate and deeply moving thing to receive as a gift.
But the time frame does make it hard to do.
I'm sure you'll do fine! Like I said, the best gifts are those that are personal. Not the typical flowers, chocolates, and teddy bears. Maybe think of something that you and him share or even an inside joke.