So here's what you do. You can make a screenshot reader app where it scans the qr code and reads it using a live side loaded cloud version of Google to verify it and then automatically switched back to graphene. Like your graphene security won't break but the Google system will detect your device as being under the generalized Google services and then once the scan is done the graphene system kicks back in.

Sorta like a vpn/spoofing system that relies on jailbreaking the Google api?