If a user wants to verify the payouts, they need to download the code and run it, yes. They can play the game without verifying the payouts though. I just need to provide a mechanism for users to verify the fairness if they wish to...
edit: Ahh! I see the issue I think you're raising. Potentially I could change the contents of verifyscript.js every round in order to cheat. So I need to prove that this verifyscript.js doesn't change. So I need to post this script somewhere (on a forum like this), where it can be quoted and timestamped by others