A nerdy kid comes in and ask for a costume that'll make him look smart. So you decide you give him a scientist costume but include a few extra changes. Like also making the new woman very intelligent as well as slutty. You also add that she has to have sex with at least a dozen different people each month or her I.Q. will start to slowly drop and wont go back up till shes had sex with at least twice that many in a month. Lastly you make her subconsciously aware of what she has to do to stay smart.
After he puts on the costume and changes into a tall sexy brunette you offer to let her follow you into the back and get her first fucking of the month in. An offer shes more than happy to take you up on.