I did this on the Havok course on Paradise Isle using the Titan. I got the first one in the caves and waited there for the others to come around again.. and I worked them 1 by 1 until it was just me and the leader. I lost.. but got the 1000 pt achievement. So close to my destroy all 7.. but oh well. Also.. remember to save your magnets up and let them all go at once for maximum effect.