Actually I'm not sure about making a non-dedicated host that actually works. However, this is how I would attempt to do it:
First make sure you have the following ports "open":
29060-29099 (TCP & UDP protocol)
Start up JAMP.exe. In the console (shift tilde) type:
net_port 29070 (enter)
Shut off the console. Then start up your multiplayer game as you normally would (make sure it's not set to dedicated).
Then see if anybody joins (again, due to the server browser bug you may have to post your server on jk3servers.com and give out your IP so people can test it).
Once in game, go to the console and type net_port to make sure its using the 29070 port.
That should be it, although you might experiment using different net ports (within the 29060-29099 range). I think (may be wrong here) 29070 is the default one needed to log into the main server list... at least for JA.