I’m not a labeling specialist, so this advice just comes from what I do know. I don’t necessarily know the best way to accomplish this, but here are some ideas:
1. Ingredients must be ordered by weight, and my guess is that the weight of cinnamon that you are infusing is quite small. If your ingredient list is such that it’s obvious that the cinnamon amount would be the last ingredient, then you don’t need to know the exact weight.
2. If you want to know the weight of cinnamon that gets transferred, something you could do is weigh the cinnamon stick before putting it in the pot, and then fully dehydrate it and weigh it again. This could be a very small amount so you’d probably need a scale that’s accurate to at least a milligram.
3. One thing that the labeling rules allow you to do is list insignificant ingredients out of order. You do this at the end of your ingredient list by saying “Contains 2% or less of cinnamon…” http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=101.4