Left handed person here. Writing is already a chore, tying up both hands just to use a fountain pen without smearing seems to cross an effort/reward boundary.
Maybe useful if you were really committed to the tool. I've been casually interested in fountain pens for a while but the downsides seem to stack up whenever I actually look into it.
You don't have to hold the stick, generally. For painting, yes, but you wouldn't have to when writing. It would just hold your hand up a little bit.
Maybe try a dowel with a glob of clay or something on the end and see?
The biggest crime to lefties is the fold-away half-size writing desk you see in lecture halls.