I use a magnet with the stock filter setup and it works quite well. I bought some rare earth magnetic discs measuring 1"x 0.125" and placed one inside the filter cover and one outside to secure the inside one.
Rare earth magnets are the strongest permanent magnets available and they both attract each other so strongly, even through the nylon (Tecamid HS or whatever) cover that they both stay in place well secured. The 1" diameter ensures that the internal disc cannot possibly get sucked into the motor.
When changing the oil, pulling off the outer magnet causes the internal one to drop right out for cleaning. I have used them for 2 changes now and both times, there were ferrous particles on the magnet. Nothing alarming, but it did seem to do a good job because after cleaning up the magnet I placed a piece of string between them and dragged the magnets through my catch pan and they didn't attract any additional particles.
I got 4 of them for $10 (+S/H) here:
Rare Earth Magnets
