Custom army card creation location

Hey does anyone know where I can create custom army cards for aotp? Much like the werewolves from the innistrad expansion I want to make a double sided army card for the eldrazi ruiner from the zendikar pack. I'd like one side to have his stats from the 1v2 rules of the eldrazi attack scenario with the other side showing his stats for the 1v4 rules of the same scenario. The reason why I want to do this is so I don't have to use the "army card" for the eldrazi ruiner that's in the rulebook.