I see, that is a problem.
The small size Bianchi Axis at my lbs had similar off-center cable routing, the manager at the shop was very frustrated because it didn't really work. One pad would always rub. I'm surprised the Felt is designed that way.
Does the Spooky spring engage the three little holes on the cantilever frame boss? If so, maybe selecting the top hole for the left arm and the bottom hole for the right arm, or some other combination, will give you the difference in tension that you need.