Local SEO Without An Addy

Well the easy answer is if he's going to meet with clients at home, to just use his home address. There's nothing wrong in doing that. He'll obviously want a dedicated phone number but if he's willing to put his home address out there then that's an option.

If not, it's possible to get local rankings without an address by just putting in the geographic area and then choosing (in Google) to hide the address. It's likely not as ideal as having a physical address, and might not rank as well as businesses that do, but it's possible.

Another option is to use something like a UPS store where they allow you to use their physical address. This is something that would be quite obvious to Google if they cared about it. And there is some debate on whether or not this works well. But it's a possibility.

And he could also consider a virtual office service. Most executive office spaces (which might be his next step) that allow people to rent one office of a much larger suite, also offer virtual services where they receive mail, answer phone calls, and allow you to rent an office by the hour for client meetings. If it were me, this is probably what I would suggest if he can afford it. It's not that expensive.

It's still possible to outrank the local 7pack in Google SERPs without an address. I'm guessing since your friend is meeting people at their homes he doesn't need to be listed on anything like Google Maps (local) since his clients won't even be looking for an address. I would optimize for everything except a street name/number (ex: City, zip code, local phone#, etc...).