Sure. A reasonable compromise would be that the app developer puts Apple's payment system in the app, for you to use, but all transparently tells you that you have to pay the 30% Apple fee yourself.

So, you'd be shown 2 options. Option 1 would be their payment processor, and option 2 would be Apple's. And you could choose to pay an extra 30% to use Apple's.

Problem solved right? Everyone gets what they want, and pays the appropriate fee.