App Rejection on Restoring Non-Renewable subscription on iOS 6 app

My app supports iOS 6 to iOS 8. It has non-renewing subscription feature with a restore button and recently I got a rejection on this:

We found that your app is using Receipt Validation found in iOS 7+ to restore Non-Renewing Subscription. However, since your Application supports iOS 6.0, Non-Renewing Subscription cannot be restored in this manner.

It would be appropriate to remove this feature from you binary and include an optional user registration feature, to deliver subscription content to all of a user’s iOS devices. Such user registration must be made optional, not required. We also recommend indicating that registering is required to access the subscription content from their other iOS devices - and providing a way to register later, if users wish to have access to this content at a future time

They are saying my app supports iOS 6 also and restoring a Non-Renewable Subscription is not possible with receipt validation on iOS 6 so create optional registration feature so user can use same subscription on other devices also.

Is it ok if I remove support of iOS 6 from my app rather than creating registration process? Will they approve if app will only install on iOS 7 and above?

As described above, I configured my app to support minimum iOs 7 made it worked. That app is in Appstore now.

Thank you.