Memo to Cher: Welcome to the dollhouse. Last month, Mattel's miniature replica of the entertainer was featured in an episode of Will & Grace in which Sean Hayes' Cher-obsessed alter ego, Jack, meets his idol. Although the Bob Mackie-clad clone (you were expecting Barbie hand-me-downs?) won't be in stores until May, it's already clicking with fans. Two weeks after the Nov. 16 episode aired, 1,200 people had logged on to the toy titan's website to request e-mail updates on the plaything. But at least one of the diva's disciples won't be shelling out $39.95 at Toys 'R' Us. Cocreator Max Mutchnick snagged the prized prototype (estimated value: $60,000) that Mattel presented to the W&G cast. ''It's in my DNA to want a Cher doll,'' says the openly gay Mutchnick. ''She's on a shelf in my office.''