I'm pretty surprised they haven't just Maliciously Complied by offering an in-app signup buried somewhere obscure in the app, with lots of big flashing warning signs saying "don't click this, it's only for compliance reasons" - and a nice discoverable easily-followable link to the browser-based sign-up. They could be continuing to make the (justified and correct!) stink about Apple's terrible practices, while also ha…
That said, I think Apple forbids you trying to redirect people out of the app by explaining that they take a cut if you sign up in it.