What about \"Paid Apps\" as Alpha/Beta testing...
I am uploading one \"alpha_version\" apk under \"Alpha\" tab... I have tagged application as \"Paid\"
It's annoying but you could just create another app in your developer console that is free and load your APK there. You will have to change the package name though and maybe give it a test name. Keep this free app in beta and then they can test it for free.
Then when you want to release it you create a new app that is paid and release that.