Configuring LCDS HTTPProxy service behind a firewall

I have an LCDS server sitting behind a corporate proxy/firewall.

I need to use a configured HTTPProxyService on the LCDS server to make requests out to beyond the firewall (can't go directly from the client because of crossdomain.xml issues)

How do I configure LCDS to use the corporate proxy on it's outbound requests?

Docs ftw:

http://livedocs.adobe.com/livecycle/es/sdkHelp/programmer/lcds/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=rpc_config_4.html

Use the <external-proxy /> tag.