If I understand you correctly, you're asking how to keep a highly-skilled person at your startup company, rather than becoming an entrepreneur him/herself. And that question is something that any company with any highly-skilled employee, in a field with low business startup costs, has to answer. And the most common answers fall in two directions: either make them extremely happy, or make them sign a non-compete agreement that they can't enter your business domain for x amount of time. The second is probably the most stupid way to handle it; you're going to cost yourself good hires who don't want to be hamstrung like that whether or not they plan to go solo. The first, keeping them really happy, requires a little more finesse.
I hear from most of my associates in the IT/programming field that they want two things from their job - interesting work, and an employer that treats them as a valued resource. If it's not interesting work, i.e. drudgery, you're just going to have a hard time retaining talent. You'll have to really pamper workers to keep them at it, and ideally give them a creative outlet (like skunkworks projects or 10% time, like at Google) to keep them happy.
Treating your workers as if they are really valuable and worth retaining is probably the most important thing you can do - people will sometimes even take a lower salary than they could get otherwise, to do cool work. Even if they will, though, the first thing an employee looks at is their paycheck, and if they feel underpaid they will feel undervalued. Perks and such are the second thing, and are what will make you stand out from the crowd (and keep your guys where they are). It doesn't have to be expensive, it's just the fact you're trying to go above and beyond for them, that they will appreciate and be more reluctant to leave. Free soda, generous time off, work-from-home arrangements, all are low-cost and make a real difference.
Of course, a lot of that goes by the wayside if you push them to 60-hour weeks; it would take a hell of a lot of money for me to take that much time away from my young children. Keep fair overtime rules and on-call arrangements, and you'll already be ahead of the pack.
Hope this long-winded speech helps!
IMHO you can only try your best to keep him interested in working with you till a limit. Perhaps making him part of your company (by giving him shares?) will instill a sense of belongingness to the company and he will be more interested in making the company a success.
Just my opinion when I try to put my feet in that developer's shoes and visualize how I might want things to be.