Here's a thought.
Someone could compose a Christmas carol and post an MP3 of the accompaniment together with an SATB score.
Each person would pick a part (S, A, T or B) and make a 320 kbps MP3 (good enough quality for single parts, but small enough to email) of their own voice singing their chosen part. Of course they would all have to be in exact sync with the MP3 accompaniment. Then each person emails in their vocal track to the organizer.
The organizer then puts all the vocal parts together in their DAW and there you have it -- the Garritan Christmas CD special bonus track!
Just a thought.