Make her earn it

"You may have my cock," the demon said. "However, I want you to go ahead and put itching powder in your sister's clothes. That will show them they are not high and mighty. I will come by your house later, and you will introduce me to Prue and Pheobe as your boyfriend."

"As you command."

The demon teleported Piper back to her house, knowing she would desperately be thinking about his cock all day.

Later that night he teleported himself to the Halliwell house and knocked on the door.