Find Java Usages within Light Virtual Files

My plugin has a specialized JSON file type whose objects may contain a property with a full-blown Java class implementation (string within the JSON). My VirtualFileSystem is able to obtain PsiFiles/PsiClasses when needed. How do I allow Find Usages for normal Java elements to show those referenced within my LightVirtualFile? For example: a helper class or method under src/main/java may be referenced in my JSON-contained Java impl, but this does not currently show up in Find Usages. I want to expose these PsiClasses to Intellij's normal Java language processing rather than develop an entire custom language.