Trying to figure out they put these balls in between the cake tiers.  Just about to buy the Cake Stackers system to make topsy turvy cake and want to cover the space and rod between the tiers.  Is there a rod somewhere here behind the balls?  how did they do this?

I would love to know as well. Looks amazing!!

There doesn't have to be a rod.  If the balls allow for fairly flat "wedges" [ < ,  > ], the cake boards could be heavily hot glued to the surfaces of several balls [all of which are touching].

You could insert dowels into the 2 largest balls and place them into the cake below so that the dowels would be vertical.  That would anchor the balls and stabilize them so that they could support the cake above.

That said, I personally think that the two top cakes may be dummies, and therefore extremely light.  I say this because of the sharper edges on the fondant.

A very cool design. I want to know what's stopping the balls pressing into the tiers below, if they are supporting the weight of the cake above. I can't see a cake board on top of the cakes (which would be dowelled inside the cakes)?

AYeah. I am pretty much unable to figure out the support unless the balls are just dowelled into the cakes.

I think that the bigger balsl are covering the support system...the ball were probably pierced to cover the pipe from the support system. 

There's no way hot glue could hold that much cake :)