Great example DrDan!
And yes Funkifized, as Matt pointed out, your need to put a chord on beat 4 of the pickup bar (in this case Bar 0) could work as shown.
That bar would have a dotted half note to take up 3 beats, then your chord on beat 4.

However, as I mentioned before, you can see from DrDan's screenshot, that this is only the PIANO track.
If you want other instruments (bass, guitar, drums etc.) you would have to do the same for those tracks.

If indeed you're going to take this over to the Wishlist (which I think is a great idea),
my preference would be to allow the user to start the bar numbering at any "cell" on the ChordSheet,
and have all preceding bars show as "minus" bars, with option of how many to display on the ChordSheet.

LLOYD S