AI navigating all 6 sides of a cube

I am doing a project where the world is essentially a cube where each face is made up of a number tiles. I am using the A* pathfinding project for character navigation. I am creating a point graph and the character moves along the top surface just fine and is able to seek selected tiles but will never use the sides even though the path is being drawn.

The issue I am having is how do I get the character to be able to navigate and walk onto any of the 6 sides of the cube?

Has anybody set something like this up themselves or have any suggestions as to the best approach to do it?