B&P shakes are part of something people call the Ultimate Cleanse and does include the lemonade but generally it is not recommended and was not a part of Burroughs original Master Cleanse protocol.
In doing the P&B shakes I found it beneficial to eat meals designed to *push* the P&B through the system and of course much water is needed. I am sure others will share their experience but I can recommend waiting until after your cleanse and not combining the two. Also follow the advice of doing one shake first and then another and working up.