Alec Baldwin is set to host the season finale of “Saturday Night Live” next week, but expect to see some other familiar faces. Backstage at the Broadway musical “Memphis” last week, “[Bleep] in a Box” singer and frequent guest Justin Timberlake was overheard telling cast members he had just come from taping a secret segment for the show. Timberlake, with girlfriend Jessica Biel in tow, was also heard telling the show’s music writer, Bon Jovi keyboard player David Bryan, that he’s interested in turning the show into a movie.