Interesting analysis of an impractical idea. Begs the question of what it would take to capture say a 100m NEO in HEO.

Article Summary:
With some patience, waiting perhaps a month or two, suitable
asteroids could be routinely found that would produce weapon
effects equivalent to nuclear weapons with yields ranging from tens
of kilotons to many megatons. With some effort, they could be
diverted to weapon using technology (and extensive supporting
infrastructure) similar to that for exploiting lunar materials,
generating solar power with satellites, or defending against asteroids.
However, at best, it would take months after a decision to use one as
a weapon to reach the desired conclusion. Because much cheaper,
more responsive weapons of mass destruction are readily available,
this one is likely to remain safely in the realm of science fiction.