I noticed that they changed the description to read Attrition/Elimination mode as well as matchmaking or custom game.
Just tested it and you can indeed unlock this with a custom game. I did this solo on Aquarius map and gave the opposing team a couple extra bots to make sure my bot team would be losing. Was fairly easy by grabbing the active camo in the center of the map and popping that when my bots started to need revives. From what I could tell, reviving doesn’t break camo.