This will be tough to do with an ASA. I'm not saying it can't be done...it may be a very manual, tedious process.
Consider adding an IPS sensor (AIP-SSM)...this will give you better visibility. IDS/IPS can deep packet inspect on application layer protocols. You can easily block IM and P2P with something like that...
You could also look into configuring NBAR on a core router, which can be configured to block P2P, for example.
Here's a link on NBAR (Network Based Application Recognition):
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...
Table of Contents 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 an...