As a side note, you may be interested about the 2D-Doc, which is a new French standard used to protect documents such as address proofs or invoice. I've been involved with it closely at work.
Every 2d-Doc include an ECDSA signature inside a 2D barcode, the key being that the barcode is a Datamatrix and not a QR code.
Basically, a short summary of the protected document is encoded inside the barcode, followed by an ECDSA signature of the summary (still in the barcode). The signature is done by an official, government-approved 2D-Doc emitter. The 2D-Code contains a short reference (a few bytes) to designate which emitter signed it, and then you can lookup the 2D-Doc TSL supplied by the French government to get all the X509 Certificates from every emitters you are interested in, in order to check the signature.
While 2D-Doc solve a very different problem than Bitcoin + BIP70, you may be interested in knowing about it as hundred of thousands of them have been emitted successfully while solving one of the problem you face : embedding an ECDSA signature inside a 2D barcode.
Thank you for your time,
Clément Elbaz