Well, this was inevitable - nothing says "hip hop" like Synecdoche, New York. The track's called "Go Hard," and it's by Daniel Lovecraft. It's actually pretty good! He name checks Adaptation, Eternal Sunshine and Charlie himself, among other stuff. That track and others can be downloaded via Daniel's blog.

Longtime BCKsters will remember there once was an entire album inspired by Eternal Sunshine - and there's a song called "Charlie Kaufman" you can download from BCK, though it's kind of oblique and doesn't reference Charlie directly. [Edit: actually, you can't download that one right now. But I'll get it back up shortly.]