This method would be useless on Showdown, because it'd be obvious that your Magnezone didn't have Magnet Pull since you can see if you can switch before your next move. If you're trapped, there will be a message underneath your moves telling you that you can't switch.
In Wifi Battles, I don't think there is a message (to my memory) telling you that you're trapped, unless you try to switch out, so the bluff would work. Though, I think most opponents would try to switch in order to test if the ability was Magnet Pull... because you don't lose a move when you try to switch, it'd just tell you that you're not able to switch, therefore negating this strategy.
Magnet Pull on Magnezone is most useful for dealing with Scizor and Ferrothorn. Ferrothorn has an even slower speed than Magnezone, making Analytic useless, and while Scizor is faster, all you need is one HP Fire to OHKO it, with or without Analytic. It's the same with Ferrothorn, because of the x4 fire weakness. Skarmory usually has Sturdy, so you will always need at least 2 moves to deal with it (unless it gets burned or something).
I'm not really sure what you're trying to achieve with this strategy. Like I said, Ferrothorn is even slower; no one invests speed in a Ferrothorn. Scizor will have speed investment, but a lot of the times it will also have U-Turn so it can switch out even if you had Magnet Pull.
I guess Analytic would be a viable ability if you wanted to use your Magnezone for something other than wiping out steel types, but Magnet Pull is the better option in OU, since you can escape with Volt Switch, should something like Heatran trap you. Magnezone's SP. Atk is high enough to OHKO most things without the Analytic boost.
