Thanks for all the suggestions, I might try them all at once and see how he reacts!
I have just thought about trying to open all of his applications (cmd+a, cmd+down), for a macbook it should take ages to recover...
haha don't worry, I wasn't intending to 'break' his computer and certainly not risk losing any files. I am quite certain that as long as it does nothing permanent there will be no problems, besides, It's a two way thing...
...If you know that person's password, you can start sharing his screen in yours and start moving the cursor when he is using it too.
or setup a bluetooth mouse. can probably use your phone