No neutral in metal switch box for three-way switches in an older 1930's home
No, you cannot bootleg neutral from the very rickety ground BX provides.
It worked for 80 years because normal switches don't need neutral.   You are introducing a new wrinkle: a smart switch that does.  Here is how classical 3-way circuits work.  Remember current flows in loops, and the route may differ, certainly as will the color codes.

Note that neither 3-way switch uses neutral, and the &quot;remote&quot; 3-way doesn't even have neutral anywhere near. Remember: installers are stuck with the colors that cables are manufactured with, so white wires may not be be neutral.  Travelers are the ones that land on brass screws, they can be any color. I prefer to mark wires with colored tape to indicate their actual function, but apparently, I'm weird.
The problem is you want to put the smart switch somewhere it can't go.  You need to rethink.
Generally, you handle this by carefully selecting a smart-switch master that goes at the switch location that does have a neutral. Then you either accept a plain switch at the remote location, or use a matching smart switch &quot;remote&quot;.  In the latter case, you re-task the 3 wires to be whatever you need for the remote to work.