Just because Joan Rivers won't be terrorizing celebs on the red carpet this Emmy season doesn't mean she's not busy. She's got a guest spot coming up on -- where else? -- F/X's ''Nip/Tuck.'' The septuagenarian plastic surgery enthusiast will play herself on the season finale of the cable drama on Oct. 5, the Associated Press reports. On the episode, Rivers requires a procedure so ''unusual'' (in the words of the show's publicist) that she evades the media glare and flies to Miami to have the plastic surgeons played by Julian McMahon and Dylan Walsh perform the operation. (In real life, Rivers inadvertently stepped out of the spotlight by leaving E! this summer to cover red-carpet events for the TV Guide Channel, only to learn that E! still owns exclusive cable rights to cover the celebrity arrivals at September's Emmys.) F/X publicist Scott Seomin wouldn't spoil the show by revealing the nature of the surgery, saying only, ''It's definitely not something she's had done before.'' Hmm, that doesn't leave much.