What I used to do when I had Steam installed on my SSD but wanted the games on my HDD was move the entire steamapps folder to the HDD and use
Link Shell Extension to create a junction point back in the folder's normal place. You can think of a junction as a shortcut in the NTFS file system itself, so that anything that tries to access the junction is seamlessly directed to the other drive instead. For games I did want on my SSD I'd just move them back onto it someplace and create another junction. There's also a program called
Steam Mover that does much the same but on a game by game basis and may be easier to use, but I've never tried it.
Of course now I got a 500GB SSD just to keep Steam and all my games on. Prices have really fallen!