The question is not, what will the business do; the question is, how will it make your boss money? If you can convince him it will make him money, he's likely to support it; otherwise, he's not likely to. First convince him he'll make money, and THEN hammer out the details. Start with a verbal pitch, then have a written proposal (short and sweet - less than a page) ready for him to look at if he's amenable.
Personally I would
sell it this way:
1) You can charge clients more for specialized, skilled services, which translates into more revenue and
profit.
2) It makes his company's offerings more comprehensive; customers interested in one service might later decide to purchase another.
3) Offer to run the new business yourself as much as possible, in exchange for a cut of the profits or a higher wage or however you think it should work. If you offer him a proposition where he makes money without having to do much more work himself, I expect he'll at least give you a fair hearing.
How do the other divisions of the business work - do they do some sort of profit-sharing or pay a fee to get the client list, or are they just hourly or salaried workers directly employed by your boss?
Can you prove your specialized skills to your boss? He may have no idea you can do more than blow leaves.