How to stop Gnome Keyring from clobbering OpenSSH's ssh-agent on Ubuntu 12.04

Recently installing Ubuntu on a new machine for the first time in a while, I was reminded of some obnoxious and potentially dangerous behavior regarding SSH agent (as articulated by my friend dkg a few years ago). In particular, Gnome Keyring is started by default, has some behavior that I don't like, and is difficult to disable in favor of the SSH agent provided by Open SSH that I prefer. The Gnome Keyring behavior I don't like is: