Include RealityKit in iOS 12 project for iOS 13 users

In my application, we want to add an optional RealityKit experience for our customers who have upgraded their OS without forcing them to do so. I was going through my code adding @available attributes to all of my classes that accessed iOS 13-specific features, but I discovered in the process that a bunch of my errors were in the generated RealityKit class files which I cannot modify. Is there any way to produce a build which includes RealityKit when the target version is below iOS 13?