You could try replacing the lemons with limes. I sometimes do a lemon/lime mixture. It switches things up a bit. Also drinking the mint tea can give you a bit of variety. Moving to orange juice or any other kind of juice would take you away from the Master Cleanse and into a juice fast. Juice fasting is still beneficial, but just not the MC. Porridge would definitely not be considered part of this fast and if you ate some, you would be starting back again at Day 1.
Just keep sipping lemonades and telling yourself how good you are treating your body right now. The "devil's advocate" (your mind) is playing tricks on you and trying to get you to eat. :)