We advertised for beta testers on the University Portal Service. 18 people requested to join the beta and about 10 have downloaded the application. We are using the TestFlight service to manage testers and distribute the application.
Beta testers create an account on the site and then register their device. We can then create a provisioning profile that allows the app run on their device outside of the App Store. We upload a version of the application to Testflight and notify the testers that the app is ready to download.