You can enter the game codes into steam and the games will be added to your steam library.
So the games will still run (or even install) without the disc after entering it on Steam? And I'm assuming that this can be done as long as the game is sold through Steam.
have you looked at no-disk patches/cracks? that's what I did with COD4 so that I didn't have to have the disk in all the time.
I think a cheap external USB DVD drive will come in handy later. you can just keep it in the computer draw so that it doesn't annoy you all the time.
normally just copying/pasting the files to a folder on a HDD works and you can launch the setup exe from the HDD, if this isn't possible maybe look into magicdisk, which creates a virtual disk drive (maybe you could have the games that need a CD inserted virtually mounted that way?
I see that we can't discuss this on the forums. But we both know this is an option. Although, rather than go through the trouble of changing games I would rather just re-buy the ones that are fairly old.