How do you change the steering rack on an audi A4 avant?

I have removed the track rod ends, the bolt under the break servo and the one under the battery holder.I have removed the plastic cover under the wheel arch to gain acess to the hydraulic couplings.Looking at the replacement rack there is provision for a third bolt centrally positioned I cannot see how to gain access to this from under the car without removing the gear box.Any sugestions would be greatfully recieved ,