How do I make app for 3rd party? Revenue setup.

Hi!,

So I want to start working as freelancer and sell apps to clients, and then they publish it, own it, etc. But I have the following question, how do they get the revenue, if I upload the game to google play myself?

I know with ads is easy, they give me their ad id and I put in the code, but how about IAP? This money is going to the uploader of the game atm, how do I do so that revenue goes to a 3rd party?

Delivering the apk so the client uploads it is not an option, because you have to setup the achievements, leaderboards, etc, within the developer's console.

Thanks guys!