I agree with others here, guys like that won't make it long term. There is a reason he is not someone else's superstar. I have heard the story too many times that the person just moved into town. It's been my experience that its more likely they got run out of the last town they were in. And I certainly have learned this from the school of hard knocks.
I also understand your need to get someone trained in and on the road. I have run smaller companies that were desperate for help and someone like this would have been a real find for me.
That's where 2 man crews will help. Once you get the guy that he is training on his own truck, get assistants for both trucks. When you hire those new assistants, you now you have the luxury to be able to get people with no experience. These new assistants (and maybe your crew leader in training) will more likely be the core of your business, not your superstar guy. Use the experienced guy as long as you can but always with an assistant in training. This will keep you from being held hostage by him when things begin to go bad. Don't get caught up in a situation where you need him more then he needs you!!
When I started with Hagopian, our MOST experienced crew leader had been with us for 9 years. 24 years later, our LEAST experienced crew leader has been here for more then 10 years. I also have more then 20 assistants that can take out a route by themselves on a moments notice. I have made lots of mistakes in hiring over the years. Having 2 man crews (crew leader with a crew leader in training) I had the ability to get rid of someone when I had to and not have a major impact on business.
I remember one year going into our slow season, I got rid of 6 people all at once. This were both helpers that were never going to be crew leader material as well as 2 crew leaders that were causing me headaches every day. One of the best and most refreshing moves I have ever made. Sure I had a lot of shoes to fill but I was able to do that because I had trained people who could step in without missing a beat.