How can I widen brakes on an '09 Specialized Transition Pro?
This part is specific to Specialized. They only make one size. If you loosen the center cable, it should have more than enough clearance for a Zipp wheel, even if you have the new Firecrest design.

The straddle clip can be replaced with a standard cantilever straddle cable and a hook, like this:



but it is not ideal for leverage on the brakes, which may reduce your stopping power. And I'm not suggesting installing the cantilever brake, only using the bridge and straddle cable.