Are you using subdomains as account keys or the account location plugin? I recently worked on a project where this scheme was in place and had to come up with a way to change the subdomain for app specific functions as opposed to account specific ones. For this particular app the user can navigate to other subdomains and to site specific pages. In these cases I wanted to coerce the subdomain which rails does not easily allow using the link_to, redirect_to, and url_for methods.

Here is the problem:

# current url: sally.example.com/stuff
link_to :controller => 'site'
# you want this => http://www.example.com
# you get this => http://sally.example.com

So I monkey-patched url_for so you can do:

# current url: sally.example.com/stuff
link_to :controller => 'site', :overwrite_subdomain => 'www' 
# => http://www.example.com

action_controller_ext.rb

module ActionController
  class Base

    alias_method :old_url_for, :url_for

    def url_for(options = {}, *parameters_for_method_reference)
      if options.is_a?(Hash) && options.keys.include?(:overwrite_subdomain)
        options[:only_path] = false
        new_subdomain = options.delete(:overwrite_subdomain)
        current_subdomain = request.host_with_port.split('.')[0]
        @url.rewrite(rewrite_options(options)).sub(current_subdomain, new_subdomain)
      else
        if parameters_for_method_reference.empty?
          old_url_for(options)
        else
          old_url_for(options, parameters_for_method_reference)
        end        
      end
    end

  end
end

environment.rb

require 'action_controller_ext.rb'