unfortunately you can't do what you want to do. Damn it would be nice, I'd have all my games here.
I know your annoyance. I have 80+ game and 5 kids and a wife that all game.
The funny thing is upto 5 years ago you could have been able to play 2 different games on two different computers.
Your Options are to use your account in offline mode
Rebuy the games
Use an Emulator to run the Steam Games sans Steam.
And I will hunt down and skin alive (Well vigorously ex-foliate) anyone that suggests using Steam Family Sharing. Then use their hide (well dried skin flakes) to make a person shaped banner that explains SFS does not let simultaneous use of different games.
I don't know of any game that allows you to move from Steam to GOG... I'd appreciate this function, but....
MAy be these? http://www.gog.com/reclaim
oh and Witcher 1 and 2.
Some games with Keys can be activated on Origin, I did that with bullet storm and some others.
And Origin will let you play different (or even some of the same) games at the same time. Score 1 for the most evil company in the world.