Super Smash Bros Brawl - Challenges?

Is there any way to get more golden hammers to break the challenge boxes. I didn't completly understand the concept of the 'only three hammers' and figured I could just get more. Here I am - doing cruel brawl - and I can only kill 10 alloys. Oh - but if you have any strategies besides jumping on and off the cliff the would be much appreciated. :)