Former majority leader Eric Cantor is now lobbyist Eric Cantor at more than double his former salary. "The veteran lawmaker "will provide strategic counsel to the firm’s corporate and institutional clients on key issues," the company said in a news release Monday night. Cantor also "will play a leading role in client development and advise clients on strategic matters," it said." http://www.latimes.com/business/la-fi-eric-cantor-wall-street-moelis-20140902-story.html
Hard to do that without making an awful lot of other things illegal (advertising, campaigning, campaign contributions etc.)
Technically it wouldn't be difficult. Politically it would be very difficult as entrenched special interests would fight it tooth and nail. But that doesn't mean it shouldn't be done. Lobbyists are integral to government corruption, therefore they should be made illegal.