Basically, you fill the first full note of the Melody track with a bunch of small C notes while having the Harmony tracks start with r1 to sync up the song properly. Here's what I use for my songs:
t120v15l64c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&
c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c
Default tempo of 120 (Though I don't think it's needed, I add it just to make sure.) so the check doesn't go too slow or too fast, max volume of 15 so I can hear it easily (Then again, almost all my songs are at max volume.), filled up by a full note of c64 fused together so when played correctly, it's just one long note, and when played wrongly, you can hear the separate notes. Now the 64th note version of mine is 137 characters which might be a bit much on some songs, so for a just as accepted, not as character heavy version, here's one using 32nd notes using only 73 characters:
t120v15l32c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c
Now do take note (Pun not intended.), even if you play this note successfully, your performance may not always lead to a perfect one, but at least it'll be played decent enough where the notes won't be noticeably played wrong.
EDIT: Don't know if you still even bother after a long while since this was first posted and I don't wanna double post, but I'm here to add another tuning variant. Been doing some work on preparations for posting my transcribed work on the new MabiMML when I did some looks at others' works with theirs breaking off 1/4th of the note for a rest. Give this a try:
t120v15l64c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&
c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&c&cr4
This should make songs that are played on wind instruments easier on the ears. Also, if you want to know, this tuning note here is at 107 characters.