Redmine 2.3 relative url root not working with Apache mod_proxy

Question

I am currently attempting to upgrade from Redmine 1.4 (based on Rails 2.3) to Redmine 2.3 (Rails 3.2). I am forced to use Apache with mod_proxy and proxy balancer, so any talk of passenger is out. I am trying to deploy Redmine on a sub-uri (https://mysite.com/redmine). The current Apache config is as follows:

ProxyPass /redmine balancer://redmine_cluster
ProxyPassReverse /redmine balancer://redmine_cluster

<Proxy balancer://redmine_cluster>
  Order allow,deny
  Allow from all
  BalancerMember http://127.0.0.1:9000
  BalancerMember http://127.0.0.1:9001
  BalancerMember http://127.0.0.1:9002
</Proxy>

I used to be able to use Redmine::Utils.relative_url_root="/redmine" to handle url_for and link_to, but that no longer works.

I have tried the following:

1. Editing config.ru

   map ActionController::Base.config.relative_url_root || "/" do run RedmineApp::Application end

2. Running rails with: RAILS_RELATIVE_URL_ROOT='/redmine' script/rails s -p 9000

3. Adding config.action_controller.relative_url_root = "/forge" to application.rb

I cannot figure what needs to be done. Any help would be great. Thank you.