You can have homebrew reside in any place you want on your hard drive. The Readme actually suggests to first install it into a directory "brew" in your home dir

You can have homebrew reside in any place you want on your hard drive. The Readme actually suggests to first install it into a directory "brew" in your home dir. You just need to adapt the $PATH in your bashrc accordingly. From my own experience: beware with moving that directory after installing some formulae somewhere else. It caused quite some trouble for me and i wound up recompiling everything in the new directory.