To avoid the painfull security in porter hall, you don't have to use the switch. You can either shoot a water arrow in it or, this I found myself, use you climbing gloves on the wall that is the closest to the fence, and then jump off, while prssing the s (the button that makes you walk backwards). when in there, climb on the thing where the artifact is lying on and use it to jump over the fence...

It's a little more effort but it is most certain worth it if you hate time limits or you want to end the mission without killing someone .