How to install Rhythmbox Spotify plugin?

Is there an easy way to install the Spotify plugin for Rhythmbox in Ubuntu 12.04?

I can only find links to recompile Rhythmbox completely and the instructions aren't very clear.

If you are referring to this Rhythmbox Spotify plugin, then I'm afraid the answer is no, there isn't a way to install it other than building the whole of Rhythmbox with it.

Also notice that the code for that plugin hasn't been touched for 3 years, so it's likely that no longer works with the current Rhythmbox code.

All in all, my suggestion would be to stay away from that plugin and use the native Spotify client instead.