Just like there's a "Gift Subs" Category (to random Twitch accounts), create an option to "Gift subs to Active Viewers" (at 5,10,15,20).

Maybe it would be easier to create a separate Tab Category label it:
"Active Viewer Gift Subs" with, 5 subs, 10 subs, 15, subs, 20 subs

I personally would prefer my gift subs be given to the viewers that happen to visit or follow a Streamer I'm following or watching...!

I'm aware your "gift sub" works on some algorithm, but you should strongly consider my suggestion! Viewers WILL love it!