Just wanted to clarify that you can use adjustable end links to increase your roll stiffness.
Normal, equal length end links transmit 0lb when the wheels are even, and transmit increasing force as the wheel travels differ. If you corner scale the car, you can use adjustable links to balance your corner weights. As a bonus, your roll stiffness starts with some initial tension, so you don't start at 0 lb, and increase from that new value instead, transferring more force per wheel travel difference, adding roll stiffness. Additionally, you can change the mechanical advantage of the link on the bar by shortening or lengthening both links the same ammount, which changes the angle between the link and the arms of the bar bar, which will add or subtract stiffness. On a road car, I'd expect you'd wear out the links and bushings quite quickly though, so I do agree with everyone else and suggest getting a bigger bar. Intelligently picking your alignment numbers might help too. Factory alignments pretty aggressively promote understeer.