Dmacmart and Ripplinger don't get me wrong by my previous reply. I did try both your solutions but they didn't work for me. I guess the magnet is just too strong. Thanks a lot still!
What I do now is turn it all the way round until it turns off. Then I manually turn it on using the slider and somehow it deactivates the sleepcover for that time, so I guess it's an acceptable workaround...
Cheers!