The only thing i could think of is left hand inside threading, but he's not
looking for a thread tool.

Boring a hole with a bridgeport in back gear? Except you can reverse
the rotation on the motor. Double chuck CNC lathe, and he needs
tooling for the finish operations in the 2nd chuck?

But it got me thinking, I don't know how to cut a
left hand thread on my manual lathe anyway. How is this done?

Simply put, spindle running forwards, thread away from the headstock;
or thread towards the headstock with the spindle in reverse. Note
that you'll have to change the relief on the cutting tool to
compensate.
--Glenn Lyford