How do I make purchases in SD on AppleTV?

I want to make purchases in SD instead of HD on my appletv because movies are cheaper that way. Can anyone tell me how to do this or if it is possible? I'm holding off on updating my iPhone so I have options like this and I still have the ability to send movies and TV Shows as gifts. Hopefully apple gets this fixed because AppleTV app is not giving you the options that iTunes app does