When I did it...I took my b&p shake....then an hour later or so had my herbal laxative tea. I'm sure it could be done in reverse as well with good results too.
Is it hard for you to drink that much lemonade because you don't like the taste or you're not hungry? Or maybe it's the time that is needed in order to make it fresh, each glass? I always made up 1 litre at a time...and I kept it with me always...just drinking when I was hungry. I kept a bottle of warm water with me too and just absentmindedly drank water when I wasn't hungry for lemonade. If the liquids are available and at your side at all times it's easier to drink 'em!