Ended up needing a quickie Pi Hat, extremely simple, but a combination of surface-mount, through-hole, and vias. I'm in the process of following the YouTube demo for ink-filled vias. You may remember I had to fall back to eyelets on milled copper, but I have higher hopes for an all-Voltera board.
One thing that would make my life easier is using the mill for the holes and final outline. Unfortunately the V1 has extremely coarse alignment for the first side. As in, yup, this won't attempt to print on the bracket instead of the FR4. So I'm stuck having to use calipers to compute the X and Y offsets of where the circuit ended up on the board, that way the mill knows where the holes are supposed to be. Calipers have their limits, plus I'm stuck using a feature nearest (0,0) and computing an additional offset. So even being very careful in measuring, the holes hit the vias, but there's noticeable skew.
I will probably get this to work, but it's a fairly clumsy workflow, even with practice. I also just realized that there can't be any skew in the V1 clamping, as I can tell the mill an X/Y offset, but not a rotational offset.
So I don't have any specific ideas on how to solve this, but it sure would be nice to be able to combine the two tools for what each does best. It's tantalizingly close.