It might be hard to keep it in sync, but it could be possible to rewrite the sample-playing code into the play routine which will be called very often (by setting the playback speed in the NSF header). It would use a counter to call the rest of the frame-based music code after X amount of iterations.

I did have the intro song partially ripped (everything except the digital), I can't find the file now.. It was a long time ago, but it seemed like it was easy to rip that part of it.