D3.js Arc Diagram - Tapered Ends

Question

I have an arc diagram that is based on this blocks example, and I'd like to taper the ends of the arc path so that they are hidden behind the circles (or at least aren't wider than the circles themselves).

I have two thoughts and I'm not sure how feasible either of them are: a) modify d3.arc source code so that the resultant svg path has tapered ends, or b) instead of using d3.arc to generate the path, create my own cubic bezier function that takes in the x and y points of the source and target nodes and outputs a a curve that tapers to maybe half of its full width? Both of which I've never done before and would be floundering a bit trying to do.

Any tips, tricks, ideas, or general well wishes would be greatly appreciated.