Find as many applications as you can which are full of viruses/spyware... (preferably download them with a linux/mac else you'll just get your pc infected, or at an internet caffe!)
Put the apps on a memory stick/cd/dvd and copy em all onto a work pc and run them, once the pc is infected so much it starts to crap blood, just point at it and theres your scapegoat! Just say it was a massive virus infection that downloaded/uploaded data.
I like this idea. While you are at it why not just burn down the building. Then they are sure not to catch you.(For bandwidth theft at least).