How about a CNC program to cut the left hand notch and safety cutout as an option to a new plastic injection mold ?
Tooling to hold the stock and machine time has to be less costly than a new mold.
I've been harassing them to do lefty inlets for years too. Weirdly they once replied that they used to do ambi inlets and stopped. In my mind that's a no-brainer. The Magpul chassis with ambi inlet seems like a fantastic idea to me, but I guess it doesn't make sense financially.