From what I'm reading, you can't do what you're trying to do. You can't have a "private" sale of apps. You can register as a business if you have a Dun & Bradstreet number and then license the use of your app to other businesses. That is possible, but if Apple finds out they will revoke your license because the enterprise developer license is for in-house only.
The only legal solution is to have each business register an enterprise account and then set you up as the developer for their account. No legal way around that, sorry.