I implemented this slightly different, and this works well for my case.
In application_controller.rb i have a lookup method which calls the Geocoder IP lookup directly passing in the results of request.remote_ip.
def lookup_ip_location
  if Rails.env.development?
    Geocoder.search(request.remote_ip).first
  else
    request.location
  end
end
Then in config/environments/development.rb i monkey-patched the remote_ip call:
class ActionDispatch::Request
  def remote_ip
    "71.212.123.5" # ipd home (Denver,CO or Renton,WA)                                                                                                                                                                                                                                                                        
    # "208.87.35.103" # websiteuk.com -- Nassau, Bahamas                                                                                                                                                                                                                                                                      
    # "50.78.167.161" # HOL Seattle, WA                                                                                                                                                                                                                                                                                       
  end
end
I just hard code some addresses, but you could do whatever you'd like here.