Exteding/Enhancing SSL Requirement plugin

I need to use SSL for a certain controller in my app. My app adapts
style and some content from the domain being called via request.host.
All of the domains are served up from apache-passenger vhost.

domain1.com is blue
domain2.com is red etc etc

However, in order to keep to a single SSL certificate I only want to
use one domain for port 443, again pointing to the same app
directory. So I would like the following redirects to work correctly:

http://domain1.com/pay/2 redirect to https://secure.domain1.com/pay/2
http://domain2.com/pay/2 redirect to https://secure.domain1.com/pay/2
- note it is still on domain1.com

# Copyright (c) 2005 David Heinemeier Hansson
module SslRequirement
  def self.included(controller)
    controller.extend(ClassMethods)
    controller.before_filter(:ensure_proper_protocol)
  end

  module ClassMethods
    # Specifies that the named actions requires an SSL connection to
be performed (which is enforced by ensure_proper_protocol).
    def ssl_required(*actions)
      write_inheritable_array(:ssl_required_actions, actions)
    end

    def ssl_allowed(*actions)
      write_inheritable_array(:ssl_allowed_actions, actions)
    end
  end

  protected
    # Returns true if the current action is supposed to run as SSL
    def ssl_required?
      (self.class.read_inheritable_attribute(:ssl_required_actions) ||
[]).include?(action_name.to_sym)
    end

    def ssl_allowed?
      (self.class.read_inheritable_attribute(:ssl_allowed_actions) ||
[]).include?(action_name.to_sym)
    end

  private
    def ensure_proper_protocol
      return true if ssl_allowed?

      if ssl_required? && !request.ssl?
        redirect_to "https://" + request.host + request.request_uri
        flash.keep
        return false
      elsif request.ssl? && !ssl_required?
        redirect_to "http://" + request.host + request.request_uri
        flash.keep
        return false
      end
    end
end

The obvious thing would be to change the code in the plugin from
  redirect_to "https://" + request.host + request.request_uri
to
  redirect_to "https://" + "secure.domain1.com" +
request.request_uri /* use a app config parameter not hardcode

However, is there a better way of re-implimenting this without
changing the plugin through over-riding the method. I hate to change
the code of a plugin as in my past coding experience this always
causes plugin upgrade issues.

Also, if I do such a redirect, would my session information be
maintained? If so I can still use my skinning logic.

Thanks,

O.