How to render geometry as volume with ramped opacity?

[papaface]

Hey，

I want to render some geometry as volume with ramped opacity.

The first picture  shows what this geometry looks like in the viewport with lighting disabled.

The third is what I have got so far.It was render with a uniformvolume shader with alpha wired into Of.

It looks almost right except the rear shouldn't occlude each other.

I have also tried to convert the geometry to volume,which took forever to get the details.

Is there any way to solve that ? or is there another approach?

Thanks!