Can't use a ProxyCommand-based SSH connection

The NAT/firewall-busting problems of issue #48 notwithstanding, mosh also has issues with the "ProxyCommand" style of connecting to machines behind NATs. For specificity, here's an example from my .ssh/config:

Host cims
  HostName linax1.cims.nyu.edu
Host mauler
  User kloeckner
  ProxyCommand ssh cims nc mauler 22

This is convenient, because it lets me type ssh mauler, and ssh will connect to linax1.cims.nyu.edu, and the 'outer' ssh run will then run over the tunnel thus set up. I understand this is hard for mosh to imitate, given UDP connections and what not, so let's assume that there's a hole poked into the firewall at port 60000 UDP on linax1.cims.nyu.edu that lets me get to mauler.

The main problem then is that mosh tries to resolve mauler locally to find the host to connect to, which of course doesn't succeed. I'd argue that it could potentially be smarter about finding the public IP of the target host--when it starts, it is executing codes on both ends of the connection after all. Failing that, I'd like to hhave an option to specify which host is actually meant.

Start by reproducing the ProxyCommand setup shown in .ssh/config and trace how mosh resolves mauler before connecting. The issue presents two possible outcomes—discovering the target's public IP or adding an option to specify it—so completion requires choosing and defining one behavior, then testing it through the NAT scenario.