As tempting as it may be, do not use a magnet of any kind - this could damage the computer.
I use a hairdryer set on cool to clean my keyboard. It gets rids of dust and fuzz, so you could try it.
Another way is to take the end off the hoover and stretch muslin or a teacloth over the end of the tube, then secure it on with an elastic band. If you put the vacuum on low setting you can hoover away without damaging the keyboard.
Whichever way you do it, wear safety goggles so you don't get spiked!