Harvey Weinstein went straight to the top when seeking advice on filling in as host of “Piers Morgan Tonight.” The movie mogul, we’re told, asked none other than Oprah Winfrey to give him some pointers before he hosted the show Thursday. Apparently Oprah’s wisdom worked, as Weinstein’s substitution gig helped make the show the struggling network’s best-rated program of the day. (Having an A-list lineup helped, including Bill Clinton, Martin Scorsese, Jamie Foxx and Quentin Tarantino.) He also, in generous Oprah style, had Nobu deliver the entire staff and crew dinner.