How can twice the work be done by a force of half the magnitude?

Work = (Force) x (Distance)

Since the calculation of work involves distance to the same extent as force, any force, no matter how small, can do any amount of work, no matter how large, by proper manipulation of the distance.

Work = F x D

or D = W / F

You want ---> 2W = (F/2) x Q

Q = (2W) / (F/2) = 4W / F = 4D

By pushing 4 times as far, half the force does twice the work.