Stacey was at the top of her game in poshness and pizzazz. But when it came to cutting a curvy hourglass figure, the svelte NYC siren came in dead last.  Until she spent nearly $45,000 getting her hips and rear pumped full of a dead person’s donor fat, that is.  “It can sound jarring at first,” Stacey, 34, a married financial specialist, told The Post. “But when you look at it scientifically, cadaver donor tissue [the process of removing bone, skin, and tendons from a deceased donor] has been