When --build-bottle is enabled, force -mmacosx-version-min=10.6

This isn't the ideal way to do this, I'm sure.  I would like to have an option that can force this kind of behavior on ENV/cc when building bottles (as I like to build bottles that support OSX 10.6-10.9), but I'm sure that you guys still want to be able to build bottles that specialize by OSX version.  What would be the proper way to do this?