eXist-db: can't start webstart client on a closed port, reverse proxied via apache

I am configuring an Apache HTTP server so it reverse proxies requests starting with /app/ to an eXist-db instance running in a Tomcat server, on port 8082. This port has been closed in the firewall and is inaccessible to the outer world. Following the eXist documentation, I have following rules in place in my httpd.conf file:

ProxyPass           /apps/  http://localhost:8082/
ProxyPassReverse    /apps/  http://localhost:8082/
ProxyPassReverseCookiePath /apps/ /

All goes well for requests to e.g. 'http://mydomain/apps/exist/index.xml'. Yet, the webstart client (accessible at 'http://localhost:8082/exist/webstart/exist.jnlp' on the web server) doesn't work behind the proxy. While 'http://mydomain/apps/exist/webstart/exist.jnlp' does generate a valid exist.jnlp file, that file can't be executed. The reason seems quite obvious: apparently, the eXist-db instance generating the exist.jnlp file only sees the proxied request as: 'http://localhost:8082/exist/webstart/exist.jnlp'. Yet, since the exist.jnlp file is executed on the client, that reference is meaningless (unless the client computer happens to have an eXist-db instance running on that port). Executing the exist.jnlp file hence fails with a 'connection refused' error.

Yet, there's no problem at all connecting a local eXist-db Java client to the proxied eXist instance with the URL xmldb:exist://mydomain/apps/exist/xmlrpc. The problem lies in generating the webstart exist.jnlp file, which seems to need access to a publicly accessible URL. However, opening port 8082 and replacing the Proxy references to 'http://localhost:8082' with 'http://mydomain:8082' IMO rather destroys the point of reverse proxying.

Do others have had success reverse proxying eXist-db on a closed port behind Apache? Are there perhaps some Proxy configuration settings I have overlooked (I'm no expert at all) that can make eXist see the original request instead of the proxied one?

Kind regards,

Ron