I took a quick look at the sources that actually pull those games and it doesn't look like it would actually be that terrible to block them, but Google certaintly didn't make it very easy.
The big question however is going to be whether or not you are decrypting traffic so that you can actually see the full URL? As long as you are then this is possible and we can work on verifying what you need to do to do so; if not then you won't be able to accomplish this.
I also took a short look at that and it looks like you could block access to:
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