hey.. i know this is an older post.. but i just had this same problem last night working on a left to right pan shot… i spent hours searching through forums.. till a compositing friend finally helped me understand how to do it.
If you take the footage and do a stabalize motion to a single or dual point (for rotation or scale) then after you have applied it the footage moves around those points. then go to the beggining of the pan add a keyframe on the position transform. moving the position so that the footage is in the center of the screen (stabilize motion only effects the anchor point not the position so changing this value will not cause problems with the stabilization) then go to the end of the footage and do the same creating a keyframe on the position transformation and center the footage on the screen. this will ideally create a even movement from left to right.. or in your case from top to bottom. you may have to scale the footage up to cover up the black.. but the less keyframes you have the more even it will be. hope this helps.. even if it doesnt help you maybe the next person who has this difficulty may use this.
Cheers
Ian