Unfortunately there are no pre-defined regexes that would help here. You would have to do some digging into the traffic itself to find out if there is anything you can reasonably filter on. Instead, you might be better off with the approach of blocking the specific ports used by the games. This might not work 100% successfully, but it would be a start. Here are a couple of links that might be helpful:
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...