Just put the 30% premium on the IAP price, same as Spotify did, same as DownDog did - sell cheaper through your own site. People who know about this mechanism, will go to your site. Ones that don’t will buy IAP or go somewhere else.
I recommend listening to the interview he did with the Verge today. He explains why he could do that but is choosing not to. Obviously, he's also spinning it to help his own argument, but he makes (what I believe are) very valid points even if he does so a bit overdramatically.\
EDIT: Link to read/listen to the interview for anyone who's interested.

Apple’s App Store fees are “highway robbery,” says House Antitrust Committee chair
Less than a week before WWDC, all hell is breaking loose in Apple’s developer relations.
