How to globally configure the ansible provisioner?

I want to set this ansible config option globally:
scp_if_ssh=True

I know that I can set it every place I call an ansible provisioner with something like:
"ansible_env_vars": [ "scp_if_ssh=True" ],

…but then my build files will be littered with that configuration. How can I set that config globally? I tried putting it in the global ansible config file: ~/.ansible.cfg - but that doesn’t appear to have any effect.