I used to work here, I'm tigersfan from that thread. I was the guy managing the Steam back end that had the achievements and such at that time. Trust me when I tell you, there's actually no way it can be done. The problem is that it USED to be something you could achieve, and at that time, there were some players that achieved it. But the game's design changed such that that achievement was no longer possible. So, what the Steam dev tools won't let you do is take away achievements from players that already earned them, which is what would need to happen here.