Just change out the tires on your 500!
I hate to say it, but unless your friend goes custom, there isn’t anything stock that will fit him comfortably. That is the price he pays for being able to change a lightbulb without a chair. I have a friend that is 6’4″ and he owns a Vstar custom 1100 custom and he dwarfs the bike. He is only 6’4″ and it looks like most people on a 250 rebel. A chopper with forward foot controls that he uses as the normal foot controls could work.
“I am the best there is at what I do, and what I do ain’t nice.”-Wolverine