The short answer is: it can’t be properly done at the moment.
If you look at the current solutions out there, they are full of holes, but it’s not easy for the users of those solutions to see that the system sucks. E.g. if you only get 30% of the actual logged in viewers, the users still think the system is working at 100%.
Twitch has a system for Drops, which is basically the same thing, but that’s for game dev companies only. There are no (public) plans to open something similar for 3rd party devs.