The new boss at Dunder Mifflin may be the season finale guest star with whom Americans are least familiar.According to The Hollywood Reporter, the show's producers want British star Catherine Tate to be Steve Carell/Michael Scott's longterm replacement -- he just left the show after seven seasons. Tate is one of a number of major guest stars set for Thursday night's season finale, which will see a laundry list of candidates hoping to take the reigns now that Will Ferrell/Deangelo Vickers' brief arc and Dwight Schrute's even briefer reign have ended.According to a tweet from the star/writer Mindy Kaling, Tate will play a character named Nellie Bertrum.