If anyone still needs the fireside card backs and you don't want to bother with multiple devices/accounts, this thing from reddit worked for me very quickly:
-Download
Evolve
-Make an account
-Install
-Login to the evolve client
-Login to hearthstone
-Alt+tab to the evolve client
-Go to multiplayer
-next to hearthstone in the list click "Find Match"
-If no one is on then just wait or back out and go to a different lobby, keep trying till you get a decently populated one.
-alt+tab back into hearthstone, go to your friends list, and scroll all the way down
-The people in your lobby will appear as nearby players.
-Challenge one of them while at least one other person stays in main menu.(Minimum of 3 people including yourself required.)
-you can concede on turn 1 three times and you'll still get the back, same if they concede 3 times. you don't need to back out of the deck selection between matches either.
basically it VPN's you all to the same IP address so it thinks youre all on the same network together. sometimes with all the people in the lobby challenging each other it goes a little haywire with the auto-declines. just slow down and challenge one at a time and give people plenty of time to accept.