AFAIK You Can't. GNOME2 is a dead project. But there are other options:
The gnome2 fork backed by linux-mint as well. I think they have finally found the way to install it side by side with gnome3.
Here is the installation instruction with much more about mate recent developments and features.
Much more info here How to revert to GNOME Classic?
Blog-Post about how it looks
Linux Mints own answer to unity/gnome-shell woes.
How do I install the Cinnamon Desktop?
Already known for its lightweightness, it has a plugin to run some gnome-applets and is not moving to gtk3 for next release. Although not the same but give similar interface.
Here are some more DE for ubuntu . See if some may fit your need What different DE's and shells are available?