Involve Kate

Jack though about it, there was no reason to buy a new bra, if he could just borrow one from his sister. She owed him, and even though it would be difficult, Jack felt that it would be a better option than having to try and buy a new one "I'll ask Kate for a bra".

Gina looked skeptically at him "Really?"

Jack nodded, "She should be home by now, and my parents should be gone, if I'm lucky".

They drove back to Jack's home and his parents car was gone, luckily enough. Jack spent a moment, thinking about how to best convince Kate that it was him, and decided to tell a bunch of stories that only he would know, the same way he had convinced Gina. He therefore left Gina in the car, since he had promised Kate that he would never share several of these stories.

Jack rang the doorbell and Kate opened after a minute. Jack started telling her about the time that she had asked him to buy condoms, so she could lose her virginity. Kates eyes widened in horror as he told her. Then as Jack began telling another story, of how she had lost all of her panties on a holiday to Hawai. She opened the door fully and motioned inside "Come in"