Just a thought that came to mind:
Can you make a similar gimmick on an electromagnet principle?
That way you could turn it on an off when ever you like, and even control the strength of it if you can build in a "high/low" switch.
Any one tried making something like that? Any chance it would be as powerful as an M5?
Edit:
I was curious so I did a small Google search and came across this:
http://www.amazing1.com/projects.htm
Scroll a little down and you will find an electro magnet that can (supposedly) lift 700 Pounds (about 320 kg)! But the unit itself only weights 4 pounds (almost 2 kg), and it works on 2 D batteries, and it only costs 80$ (about the price of an M5).
So I wonder if you could make one that has a fraction of it's power, for a fraction of the weight, for a fraction of it's cost, and get yourself an M5 for less money, and with an ON and OFF switch.