As of cPanel 11.23, proxy functionality has been restored internally without the need for the old cpanelproxy.net script that stopped working after 11.18. Full instructions are here:
http://www.v-nessa.net/2008/07/26/setting-up-cpanel-proxies
In short:
- Upgrade to cPanel 11.23 if you have not already
- Enable the three proxy settings in WHM > Tweak Settings
- Install mod_proxy if it is not already installed, preferably through EA3. Vanessa at v-nessa.net includes instructions for installing the module separately if you do not want to reinstall Apache.