There is nothing more to be done without LSD. If you stiffen the front or soften the rear, you simply make the car push more forcing a lift of the throttle. In the end, it will slow down your lap time.

Your only approach is to use throttle control to get as much as you can get without spinning the inside tire too much. Actually a little spin can help rotate the car but not that much. You can only do what you can do so be aware of the spin and minimize it.