Okay how about this. Attached is an example where you give an array of Bar Plot values, and a gradient graph is generated. It uses the gradient code I posted earlier, along with code to get the colors of the plot, and find their positions for replacing. It is somewhat robust in that the plot size and positions can change and the new gradient overlays should be placed in the correct locations. At the moment only positive values are supported. If you really wanted I think you could give the 3D look with some minimal effort. This is all using the picture control overlay feature of the graph, and on initial creation you can see the flicker between the normal solid bars, and then the overlays.
Gradient Bar Plot.zip