I was thinking of doing this with my extra set of SC wheels. The plan was to take the tires off, then mount the wheels to the rear of the car while jacked up. Then have the car idle in an appropriate gear (2nd or 3rd) and with the wheel spinning, lay a hacksaw blade on it. It should cut a straight and smooth groove. Before it's all the way through, start another groove 2" over.
Then, when the grooves are almost but not all the way through. Stop the wheel, take it off, and then cut the rest of the way through. Then cut the other wheels taking a 2" section from the another one and just cutting one groove in the other two. Then you could just get them welded back together the way you want them. It would be good to balance them without tires using a grinder on the inside before you mount tires on. The reason I decided against it is because I wanted to weld together the wheels with the 2" section removed as skinnies for the front. But they don't make skinny tires in a 16" or at least I couldn't find any.