you are correct if you search on you tube how to unlock steam achievement or something along those line you should find your self a software!
The software allows you to unlock achievements on any game on steam but also aslong as the software is open and a game is selected it shows on steam that your on the game even though your not. I mean your PC must still be on but i mean you don't need the game running the whole time.
I would link you but dont think i am allowed too!
not sure if I am allowed to even say what I just told you :/
its our secret
I cast the invis from MOD spell on this post