Completely hide use of PackageManager in the generated code

Analyzing the apk with Android Studio, in classes.dex every call to native methods aren't obfuscated, also for explicit Class identifier, e.g.:

.line 3
    invoke-virtual {p1}, Landroid/content/Context;->getPackageManager()Landroid/content/pm/PackageManager;
invoke-virtual {p1}, Landroid/content/Context;->getPackageName()Ljava/lang/String;
...

I'm writing a code to access PackageManager via reflection, in order to make harder the work to find its use in the generated code.

This is a portion of code that works in my Android application:

import static com.example.test.Utils.getPackageManagerViaReflection;
...

public class MainActivity extends AppCompatActivity {
    ...

    @Override
    protected void onResume() {
        super.onResume();

        PackageManager packageManagerViaReflection = getPackageManagerViaReflection(this, this);
        ...
    }

    ...
}

The method:

public static PackageManager getPackageManagerViaReflection(Context context, Object callerObj) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    String getPM = new String(Base64.decode("Z2V0UGFja2FnZU1hbmFnZXI=\n", 0));
    Method gpmMethod = context.getClass().getMethod(getPM);
    Object gpmObject = gpmMethod.invoke(callerObj);

    if(gpmObject instanceof PackageManager) {
        return (PackageManager) gpmObject;
    }

    return null;
}

How to completely hide the text PackageManager in the cast (PackageManager) and in instanceof PackageManager?

Thanks a lot!