I've had 4 surgeries and 3 of them I ate crap before and after and I healed fast. My last one I was doing a keto diet and was in ketosis before and after the surgery and I felt fine through all of them shortly after waking up and without any drugs. So if it were me, I wouldn't see The Master Cleanse being much harder on someone's system then eating crap..which most americans do anyway and they all have a lot of surgeries just fine. Obviously the lemonade is more nutritious than pizza and chocolate.
I know a kid who just had his tonsils removed. He's been living off of Mcdonald's shakes and Ben&Jerry's for 4 days. And he's otherwise fine except for a sore throat. I don't see how lemonade would be much worse than that. So go figure.