This should be possible now if you don't mind getting your hands dirty and don't overload the instance :-). Cc'ing Coren to give his administrative okay; the rest are directions for green lights:

1. Log into tools-webgrid-01.pmtpa.wmflabs and take a look at /usr/local/bin/tool-lighttpd (that is called by "webservice start"). It basically starts /usr/local/bin/portgrabber with "$tool" (the name of the tool a webserver should be started for), "/usr/local/bin/lighttpd-starter" (the program to start) and "$tool" (again; this time arguments for lighttpd-starter).
2. portgrabber takes to the portgranter on the local host, sends it "$tool" and gets a free port number in return.
3. portgranter sets up tools-webproxy to relay requests to "tools.wmflabs.org/$tool/ to a webserver on that port number.
4. portgrabber then calls lighttpd-starter with the argument "$tool" and the added port number which starts a webserver on that port number.

To braid in Netty there (or any other thing that speaks http) you need to make a wrapper script that takes the port number as its command line argument and starts up a Netty instance on that given port. Then you submit a job to the queue "webgrid" with the command "portgrabber wrapper-script". This will start portgrabber on webgrid, that will start your wrapper script with a free port, and this can then start Netty.

Don't use the normal webgrid for that, but use the tomcat queue. The normal lighttpd queue are /severly/ overcommited under the presumption that nothing but lighttpd runs there.

A (possibly) better model is to look at tomcat-starter and tool-tomcat.

That said, this is now a "normal" scenario and in use by some tools. The exact process is available:

https://wikitech.wikimedia.org/wiki/Nova_Resource:Tools/Help#Other_web_servers