from last article:
"In the same way, the team's paper, published in the March Astrophysics and Space Science, shows how Earth's orbit can be increased very slightly if a suitable asteroid (or any object about 100 kilometers across and weighing about 1016 metric tons) can be made to fly in front of Earth as it moves in its orbit."
About 1016 metric tonnes? I think someone dropped a billion or trillion. A 1000 metric tonnes is nothing- a rock 10-20' in diameter. It's a pretty screwy idea in any case, but you could get same thing if you have some law which encourages importing material from NEOs to Earth- like a tax benefit if material nets orbital energy- and a penalty if you take orbital energy away from Earth.
-gb