OK, since you understand the reasoning behind order headers
(they belong to orders not subjects) and are able to print subject
keys in a list format as described alsewhere I won't repeat all
Theoretically if we can print subject keys we should be able to
print barcodes - it's just not a feature that has been implemented.
But therein lies the answer as well for now. Why not use a text box
with a barcode font?
Great idea about the font. I never knew that was even possible.
So it took quite a lot of tooling and trial and error to get to where I want, but I was able to get a subject barcode on the order header. It's not very elegant at all, mainly when there are multiple packages in an order, it gives me multiple barcodes as well and the formatting gets really bizarre, but after a few tricks I got it to look pretty decent.
In it's current form, I'm not sure how you could handle this differently. And I don't know how much demand there is for a change to how headers work. We always seem to be a special case with everything. :)