I was chatting on irc and organizing my wallpaper when I realized that there was no way to set my background image directly through Nautilus. I cracked open Anjuta and got to work.
Here is the result: nautilus-wallpaper
I still need to wrap my brain around autoconf, automake, etc. I did manage to hack the Makefiles so that the extension is installed to prefix/lib/nautilus/extensions-1.0. Hopefully there aren’t any other quirks with that.