What's the easiest way to break into show business? Have a friend or relative in the movies, of course. The recent video release Coneheads is a case in point, so to speak. Dan Aykroyd not only knarfles the Garthok but also shares the screen with at least three other Aykroyds and some longtime pals he managed to squeeze into his earlier movies. Freeze the tape in your VCR just as the invading Conehead force makes a U-turn, and you'll catch a glimpse of nonactor Aykroyd buddy Laurence Bilzerian-who's also one of the two guys on motorcycles seen near the beginning of Dan's 1991 directorial debut, Nothing But Trouble.