I would just assemble the mix tape in a montage and then render individual numbered mp3 track files from it. The iPod should be able to deal with that, just like it would any other continuous track-separated album in the iTunes store (like a live album, or an album with crossfades between every track). Those types of albums aren’t sold as one big file, they’re sold as individual track files. If you could make one long MP3 with track markers in Wavelab (can’t remember if you can) I doubt the iPod could cue to those track markers properly anyway.