We run Ubuntu on a lot of the department computers, and some things are easier to configure via their appropriate GUI than they are from the command line (sigh, :p). I don't have to do this often, so often I don't remember the interface, or even the name, of the app required for the particular configuration I'm try adjust. Ah, I think, if I was only sitting in front of the computer in question rather than logging in via SSH, I could click on the Preferences dialog and it would be right there. Wait, why should it matter what computer I'm sitting in front of? Enter nested X servers such as Xnest and its successor Xephyr.
The problem with running a remote desktop or windows manager is that when you fire up your local X server, you usually also fire up a windows manager to manage it. If you try to run a remote windows manager, there will be two managers trying to manage one server, which can be problematic. Xephyr lets you start another X server nested inside a window of your main X server, and you can then start the remote windows manager in the Xephyr window. Basic usage looks like this:
home$ Xephyr :1 -ac -screen 800x600 2>/dev/null & home$ export DISPLAY=:1 home$ ssh -YC hop1 hop1$ ssh -YC hop2 ... hopN$ ssh -YC target target$ gnome-session
Don't forget to kill the Xephyr process once you're done with it.
Of course, with all the X forwarding, it doesn't actually matter which host Xephyr is running on. However, it may be easier for you if you only have to install it on your main computer. See Igor Ljubuncic's Xephyr tutorial for a more detailed explanation of the whole process.
In order to install Xephyr on Gentoo, you'll need to (re-)emerge
x11-base/xorg-server with the
USE flag enabled.