I had a local framebuilder braze 2 cogs together; the first flipped, then a steel spacer, then the second with the second cut out so it slips over the threaded portion of the first. A 21-17 "dingle". I also put a touch of dish in the wheel so those two cogs line up with the first two chainrings and the other, now dished out, lines up with the outside chainring. Works really well. Each ca hainline is a rock solid, simple fix gear, just three very different gears.

Ben