A bit late, but did you consider making ~ 3/4" spacers for under the pivot bushing brackets, then extending the 27mm bar and adding a 2nd, softer hole, making the lever 3/4" longer? See more at your car prep thread, including RSB options and rates...... both of my off track excursions last year were because of the rear breaking loose. I've done all I can with the 27mm rear swaybar to get it a bit softer. So, as much as I hate to, I'll be trying a smaller diameter rear swaybar.
Next event - April 14th.