seriously, you could add a spring soewhere along the pushrod, where it would be convenient. The weight of the wheels will nuetralize the spring of course, so it shouldnt hurt anything that I can think of. Seems I would add an achor on the rod, and conect the spring to a fixed point, in the direction that will pull the wheels up. Now that im thinkin more....it may affect the down lock, but if the servo travels all the way to the lock position, iI dont forsee a problem. Hope that helps!
d