Stopping the (probably multi-axis) rotation of a rock could be done a few different ways. A small nuke would work. An impact from a different, smaller hunk of Solar System debris would work, and would be within current technical limits.
https://freerepublic.com/focus/chat/4296982/posts?page=22#22
There is a lot to be said about a pure impact (heavy mass) impact. But, in addition to the obvious need to verify the asteroids actual mass and precise orbit so the need for changing the orbit at all is determined, we need a good vector for the fragments after the impact is known.
Last I heard the mass was uncertain by a factor of over 8. Total kinetic energy uncertain from 5 Megaton to 90 Megaton.
(Boeing should change its current go-to-the-moon-with-a-manned-rocket, and reprogram its failing big booster program. Otherwise, SpaceX will grab this contract too.
A simply flyby (or two) will test the long-range, deep space process. After a flyby (and Orbital refueling process works), then small impactors to determine mass of the rock are feasible.