I have researched this a lot. It is easier with the modern sunrace produced hubs but the idea is to somehow lock the planet cage and the hub shell together. There is a method based on hand file work. Post in thread 'Sprocket Size'
https://motoredbikes.com/threads/sprocket-size.62840/post-664663
A good picture of an aw hub shell ratchet.
View attachment 226795
I have read a claim that with a cut off wheel you can use the method that is typically machined. Said individual has no pictures on it and last posted over 5 years ago on. A strong rotary tool with a thin cutoff wheel and a steady hand would work best for this.
View: https://www.flickr.com/photos/tags/2speedfixed
If you can source a center punch and drill hard enough to get through chromed, case hardened steel, you could pin the hub shell and planet cage with roll pins.