I recall installers always asking you where you want to install things. Sometimes, that's hidden behind "custom install" or something like that. Is that not the case anymore?
By telling it to install to d, e, f, or whatever drive you want in the installer. You may have to choose the {advanced install options] for some programs, but it's always possible to change the path of installation.
In steam at least there's a setting to add a separate steam library at another folder. You can make that folder on your other drive and then have new games install there by default.