Park a ghost in the middle of a wall on one of the bases that has room on top in between the pillars to fit the
tank. Make sure both tanks are in position just about directly behind the ghost, and drive one straight at it.
Once it runs itself about to the lip of the top, ram the other tank into it full speed and it should fly up
there. It may take a few times to accomplish this.
The tank gunner is nearly immune to snipers in this position.