I think that one could fix this by removing the shift lever and building up the spherical area that contacts the shift rails with weld and regrinding it spherical again. I know this was done commonly by Model A Ford restorers back in the day.
You would have to look closely at the shift rail slots as well. If they are worn they may need to be built up.
As I mentioned earlier, paying attention to your shift will avoid this lockup while you prepare yourself for the permanent fix. It is a lot of work to remove the transmission top cover!