There is another way to achieve this (but apparently the developer didn't do this). Make a second version of the app that requires a login. Give the login info

There is another way to achieve this (but apparently the developer didn't do this). Make a second version of the app that requires a login. Give the login information to your supporters. IIRC you can even put an app into the store and set it not to appear in searches(?), then you need also to hand out the iTunes url.