Yeah i suppose it could be done:
power - just get +12v from anywhere which comes on with the car, ie radio/heaters.
switch - 3 way (On-Off-On) double pole toggle switch with spring return to centre,
folding motor - from a breaker/trader?
Then connect the +12v and negative to the middle two poles on the switch (off), then connect +12v and -12V to one side of the switch (on) and then the opposide on the other side (on).
This way, when you press the switch to the left, it would operate the motor forwards to open the mirrors, and when you press it to the right, it would operate the motor in reverse, so the mirrors would fold in.
Hope you understand what i mean, this is how i wired up my electric aerial, so i have full control of its position