Do you have any idea how analytics work in this day and age? How do you think google, facebook and youtube show you ads, they randomly guess your tastes and interests? No. This is called data gathering so you can cater content for your users. Next you're going to tell me that that there aren't websites that don't track what you look at in order to toss you some ads related to what you've been looking at.
Also, OP said he wants to see unique players and not stumbled-across viewers, not to mention that how would you even spam them? Look at their profiles and hope they've commented on another game or community thread just to reply to them "HEY I SAW U R PLAYIN MY GAME. HAHA. U SHOULD GIV ME FEEDBACK."? You just sound like a troll.
In any case, itch.io offers Google Analytics support so you can track even more data than the basic one itch.io provides which honestly is a bit lackluster and sometimes isn't even accurate.