Build A Faster Car - helping drivers engineer

Greetings fellow gearheads and engineers.  Quick question:  How can I calculate the rate of my swaybar if my cross section changes?  This is for the front of a Saturn, which has an odd swaybar that also serves as the front half of the control arm.  I'd like to weld a sleeve over the center section of the bar to increase the roll rate.  I understand that will increase stress in the non-sleeved sections of the bar, but I'm more concerned with how I calculate the rate.  I know its not that complicated, but my education or brain is failing me at the moment :(

Edit, my image seems to work in the preview pane, but not in the actual post :(

URL:  http://s12.photobucket.com/albums/a216/ProDarwin/?action=view&current=SW...