I have installed emacs with homebrew, with the --cocoa flag, which makes homebrew create an .app bundle in /usr/local/Cellar/emacs/<version>/Emacs.app. I have symlinked the .app bundle into /Applications/, to make it easy to open. The problem is that when I try setting file associations for files, I can't set Emacs.app as the default (the Add button is greyed out):

Now I could just copy or move the .app bundle into /Applications/, but that would require me to copy it over again every time emacs is updated via homebrew. Is there some other way to solve this?
