AFAIK, you can create a digital agency and make a deal with google adwords, yahoo ads etc and you can publish your customers ads on those publishers and you got paid in bitcoin and pay in fiat money.
There're over 36.000 ad network that uses google's adwords service. But I'm not sure that google accepts this kinda service.
Adwords definitely does not accept my business (I checked!). I think your suggestion of creating a digital agency would be workable if they did; we could even go direct with google if they did. I've come across some big adult website ad networks, but have found them to be surprisingly archaic with payment types and feature sets.
This is one of those "Shut up and take my money!" experiences!
If you don't institutionalize your business none of the big networks will accept you. I guess you can try something like that:
Buy or collect adwords/facebook coupons and advertise customers' websites with your personal account, but I think you need to be adwords certified or at least you need to become a verified advertiser.