Pretty sure you're stuck with ME7, unfortunately.
Also, keep in mind that the IMEI and S/N are tied to the board, so you would be sending back a phone with the same IMEI and S/N as the replacement instead of the defective phone. It might cause problems.
Sent from my Nexus 7 using Tapatalk 4
Current: Galaxy S4 [VZW]
Past: Droid RAZR Maxx / Galaxy Nexus / Thunderbolt / Moto Droid / TMo G1