piggyback off (of) (something)

To use something said or done by someone else as the foundation for one's own actions. A: "It's interesting the way Hemingway portrays Lady Brett Ashley doing things more traditionally associated with men, such as frequenting bars and having sex with various partners." B: "Absolutely. To piggyback off of what you're saying, I think the character can actually be read as a symbol of the feminist ideal of the New Woman." They're not really your friends—they're just trying to piggyback off your success so they can launch their own careers.