Might this work?
/cast victory rush
If you have either your slam proc or your victory rush proc available then it will use one of them. If victory rush works out to be a more powerful attack than slam maybe swap the order round in the macro.
Also - thinking about it - at present victory rush costs zero rage. This is necessary because it's an opener and you need to use it at the start of a fight when (you guessed it) you have zero rage. Does this mean that one of Fury's three main attacks in Cata will be resource-free? Or will they change the talent to allow victory rush in combat, but make it cost (say) 10 rage?