Thank you for the reply.

I eventually achieved the effect I was going for by creating an extra doughnut chart slightly larger and with a 0% doughnut hole size. I made the outer and inner rings transparent as well as the background. I layered it over the main chart and it worked well. Before that, I tried experimenting with multiple rings but the outlines seemed to be making it look wrong. Perhaps I didn't spend long enough tinkering with it. Thanks again!