How to reflect on a class from an imported package with a private constructor?

I am using the reflectable library to reflect on types from imported packages (like analysis_server_client or flutter). I can reflect on types that have public constructors like Notification or Request (from the analysis_server_client package). I reflect on those types by extending those types and then using the superclassQuantifyCapability capability.

However, I am not able to reflect on types that have a private constructor like Icons (from the flutter package) since I cannot extend them. Is there a way to reflect on types like Icons that have a private constructor?