I pulled some copper up from the edge so I could get a reliable connection.
I used sand paper to remove a patch of soldermask from the back of the board. After placing a piece of clear household tape over the bare copper, I cut out the negative of a small sample circuit. Sadly, I don't have any pictures of this process, only the before and after shown below
Salt bath (vinegar; the blue tint is from copper ions left from a previous electroplating)
On the first try, I made the gaps too small. Additionally, I neglected to remove all soldermask from the area, and I scratched the PCB with a screw driver. All together, this made for a badly etched board.
The board after a second try. I made the separation as wide as possible to ensure success.
The other side of the PCB. The leads on or near ground were removed, others were largely untouched.
Grinding wheels are no good at removing soldermask.
I'm not sure I could have chosen a simpler circuit, but I was still stoked when this worked.