Darien-l,
This question came up earlier whether HC microwave popcorn sold in boxes of 3 could be separated and mailed in as 3 UPCs. As I recall, the ruling was as long as the single item does not say "Not labeled for individual sale," and you have the gazillion register tapes to back them up, it's a valid UPC for the promotion. I say, Go For It!
Here's the granddaddy thread started by Counsellor:
http://talk.flyertalk.com/forum/Forum1/HTML/001021.html and a followup thread on receiving certificates started by countryboy:
http://talk.flyertalk.com/forum/Forum1/HTML/001363.html