I get all the horizontal nuts close enough that I will be able to get at them with a small allen wrench for final alignment. The verticals, I just start onto the screws and slid them in from the top of the rail. Taking them back out, I just ensure I don't remove the vertical screws completely, only enough to loosen and slide the panel up.
On one occasion, I did "drop" a nut to the bottom of the slot. The magnet idea would have been handy then. We'll see if I can remember that next time