GROUPS that hand out awards can be suckers for acting stunts... The tradition is so entrenched that Kate Winslet, playing an outrageous comic version of herself in the HBO series "Extras," listed a surefire way to get that elusive Academy Award. "Daniel Day-Lewis in 'My Left Foot?' Oscar. Dustin Hoffman, 'Rain Man?' Oscar," she says. "Seriously, you are guaranteed an Oscar if you play a mental." Irreverent, imprecise (the Day-Lewis character was not mentally troubled) yet essentially true.This season she might have added: playing gay. There has been an explosion of Oscar-baiting performances in which straight actors play gay, transvestite...