Hmm.. could be done, although it would have to overcome a few hurdles. (Please understand that I'm not trying to rain on your parade at all.)
The magnets would have to have a strong enough attraction to overcome the resistance of the turnout mechanism. I believe that the Peco turnouts also use a spring to ensure the turnout stays locked to one side. A hand-held electro-magnet might work, but then it would be attracted to anything else magnetic, like the rails themselves.
Also, the turnout-mounted magnet would have to be far enough away so it doesn't interfere with magnetic couplers or metal wheels/axles.
I really like the idea, though. It gives you a way to operate distant turnouts without melting mechanisms, stationary decoders, or cables running under the layout. Lets you keep costs down and not have to walk around the layout to throw a switch.
Keep thinking up stuff like this! It's the ability to introduce new ideas that keep this hobby dtrong and fresh.