Just an update if anyone is interested/gets into the same situation.
I cleaned the hub body threads and 10mm steel bolt and then put some light oil on them. As you know the hub body is aluminium and the threads are quite soft.
I just used a big hex wrench and a lever to slowly turn the bolt into the hub. I would go a little ways forward then back out. I cleaned it out a few times and re-oiled it.
I had no problem attaching a new freehub body to the old hub (Uniglide > Hyperglide) and after this procedure it screwed in tight on it's own.
I would not trust this for hundreds of miles but it'll do until my new hub arrives.
BTW I tried making a tap out of the bolt with a triangular metal file I had laying around.... there was no way that was gonna happen at least by hand. The bolt material must be heat treated, it is hard as a fricking diamond. I could have done it with my dremel (crudely I am sure) but why bother since this worked fine.
Once the bolt was all the way on the freehub was perfectly straight.