Why won't it shift into last gear until warmed up on 2009 Toyota Yaris?

Why won't it shift into last gear until warmed up on 2009 Toyota Yaris?
The engine has to be at a minimum operating temperature for emissions purposes. By holding the transmission from going in the last gear (overdrive) it keeps the RPMs up and the engine heats up faster. Usually occurs when the outside temperature get below 50 degrees.