How to get an iOS app for a web SaaS product approved?

I'm working for a business-to-business SaaS startup that has had a web app for a few years. We want to release a supplemental iOS app for the product. The iOS app is only intended to support a subset of the full functionality of the SaaS product, and cannot function independently without an account on the web app.

We have had a few simple releases go through the approval process just fine, but now Apple has stopped a release, asking us tons of questions about how users get accounts and how they pay. We're answering them honestly, but Apple seems to be pushing us towards using the App Store for signing on new accounts.

This is simply not an option: our product costs thousands of dollars a year, and we can't fork over a chunk of that to Apple, especially since the app is an appendage to the main service, not the full service. We'd sooner not have an app.

What options do we have? Are there specific answers that they're looking for that would get us past this stage? Are there changes we can make to the pricing model or to the app itself that would make Apple happy without losing 30% of our revenue?