Unless you want to get into rewiring the mill the easiest/cheapest solution is a static phase converter.
I’ve bought several from
Static Phase Converters A static phase converter is used to generate 3 phase power during the starting of a motor. A static phase converter consists of one or more start capacitors and a start relay. The start capacitors produce electricity across the third winding of a motor during start up,
www.northamericaphaseconverters.com
And been happy with the service and performance.
Yes, he will loose some power but it’s unlikely he’ll notice the difference in a hobby shop. If he wants to go with a rotary converter later all it takes is a used 3 phase motor to convert the static box.
John