must using GameActivity to interact with UE in Android?

when I export a demo android project from UE4.5, I found that UE use NativeActivity(GameActivity is child class of NativeActivity) to interact with Android.

but my situation is that we running as a server to render with UE, we won’t show it out right now and we pass the rendered surface to client to display, so we don’t need a NativeActivity at all, we want to call method in libUE.so directly to trigger it rendering, anyone know how to implement it ?