If a lift is out, there is no plan B for a disabled person to exit from platform 2. We just know that at least one will be out of order for enough of the time to make the service unreliable.
A better solution as we all know, is making an exit to the car park.
But if that is not possible, then why not construct a long metal ramp starting from where they are currently tipping the dirt into the ~xmas tree yard (the wall sticks out 6' here), all the way to the bottom of the stairs. (replacing the steep stairs from platform 2).
I believe there used to be 2 staircases in this area, so it is not an entirely new idea.
Any money left over could be used to install a lift in the pedestrian underpass.