kiriba-ru’s triple spacers would probably work with the included pill: Low-cost copper pills, spacers, optics, drop-ins (Updated 23/10/2022))
I am probably going to try and make my own and then solder it to the included brass pill. The whole body is copper, so I can’t imagine the pill being brass would hurt it. I was going for overkill with a copper pill, copper DTP MCPCB, copper host… but it should be just fine with a little brass in it.
The spacer shape is pretty simple, and a small piece of copper rod/bar would get me most of the way there.