Hi Max,
I had a go at this a while back using Fontlab, but relied on a loophole that allowed the creation of fonts with unclosed curves. An upgrade closed the loophole (and the curves!).
It proved to be a frustrating quest and in the end I got too busy to reach a successful conclusion. There’s some dialogue that might be useful to you in Are there any single line Fonts? - #31 by jeremy5. Maybe when things get less busy I’ll get back to it.
Memory may fail me, but I seem to recall that it will be necessary to work with McNeel to include your single line font in a list of such within the configuration of Rhino.
Regards
Jeremy