Quaife or Torsen differential? Stickier tires? Glue Nerf balls to the gas pedal?
Perhaps get the correct ABS module and enable traction control? I don't think anyone here who's serious about performance considers traction control to be a performance enhancement due to the way it was implemented in these cars, but it's just a suggestion.
I'd want a better differential before I'd even consider TC. I've driven torque biasing Quaife and Torsen diffs in front and rear drive cars, and the before/after effects are stunningly trans-formative.