I stand corrected - "the other Heather" lives in Calgary.
Probably I can use a "flat rate Priority padded envelope" between myself and the host, and probably your trades would fit into that OK. If so, then I have no extra cost to relay your seeds, since the padded envelope is about the same price as a small Priority box.
The only problem would be if getting through customs on the way to me slows down your seeds so much they're late for the swap.
So I would be happy to do it, just let the host and I know.
If you worry about paying back favors, and "any Heather from Canada is a friend of mine" doesn't cover it, maybe some day post a photo to one of the "chicken" threads in the Farming Forum, or start a pot-bellied pig thread.