Do as John says, NBAR is the solution to this. However, I recommend that you don't actually block it, just give it a VERY low bandwidth. That way the users do not waste time trying to get round the problem, but it is very frustrating and they actually stop using it. Done this successfully at a couple of schools, and the stats show almost no P2P activity after a short while.
It has been a while since I actually configured this, so can't remember the exact method. But CAR sounds about right. Make it so small that even a small file will take a couple of days, and they will give up. Good-Luck.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...