I have a method that is almost unfailable, the things you need are level 5 time stop and level 3 inferno, I organised my magic like this:
5 Time Stop
4 Time Stop
2 Time Stop
1 Time Stop
Now, what you do is when the speaker says: "Three..." You start charging a level 5 time stop spell. Release it when he says : "One..." So that it is active when the timer starts.
Keep charging level 5 time stop spells, then start attacking the beetles that spawn. Make sure you keep level 5 time stop active. Inferno is a nice way to damage a lot of enemies at once.
When there is a flitswitch bonus, hit it and continue killing enemies. This way you´ll most likely end up with a score of 100.000 or higher. This will also get you the ultimate prize.