1- fill your tank with petrol
2 - go to Super Highway
3 - put some classic rock music on
4 - gun it
In all seriousness, this is the most effective way to clean the cat, unless it is so clogged that the engine will hardly rev. That doesn't seem to be true in your case. So, just go out for a drive on a long open road. About 20 km of driving at 4k+ rpm will clean the cat real good. Make sure the engine is completely warmed up first.