Just register 3 different apps and create a yaml file with those keys (social.yml). Something like:
development:
fb_key: 123
fb_secret: abc
production:
fb_key: 345
fb_secret: def
Then create a global variable of it in an initializer:
SOCIAL_CONFIG = YAML.load_file("#{::Rails.root}/config/social.yml")[::Rails.env]
This way you always use the right key for the environment your in.