How to make a derailleur work in opposite directions? I am making a bike for a school project that can switch between upright and pseudo-prone position. It has two sets of crank assembly; one on one side of the rear gear set and one on the other; the task is to be able to switch positions. 
However, the problem is that when you use drive train for one position, it works fine and the derailleur can change gears easily. But the same can't be done for the other position because the derailleur only works in one direction. 
One potential solution is to fix one gear(the biggest or the smallest) for one position and switch the other gears for the other position. 

Could someone please help me fix it such that all the gears can be used in both positions?

Here's a picture of the bike's design to explain:
When you switch to the crankset behind cogs, you need to move the derailleur above the cogset. 

Think of it as rotating the entire drive train 180 degrees forward or flipping the entire bike over the bars and then moving wheels down until they touch the ground.



Note that the different crank positions require different chain length.