Rendering equipment overlay sprites

Rendering equipment overlay sprites

Alright, not quite a modelling question, but there doesn't appear to be a rendering board, unless I'm going insane.

So I'd like to create a unit with multiple pieces of interchangeable equipment, rendered as sprites. However, I don't know how to have the obscured portions of an overlay be rendered transparent - see OSARE's equipment spritesheets for a good example, where the portions of weapons covered by hands are not shown.

This is probably a fairly simple thing, but I don't know how I'd search for it, and I hardly touch anything outside of modelling in Blender (or any program for that matter).