You can't neutralize a component, but a solar sail vessel would not need to: diverting a fraction of the force retrograde (without neutralizing the rest) would be enough to turn a stable orbit into a spiral towards the sun.

Edit: But the way I understand the plasma magnet drive it would not be able to divert the force vector at all. It could still travel in both directions by modulating the throttle after using other means of propulsion to "replace" some orbital speed with solar drag, but it would never match the speed of its orbital peers. Maybe useful as a complement to conventional solar sails ("solar spinnaker")?

To put it another way, my reading of the article is that it only provides an acceleration vector directly away from the nearest star.

That can be used for propellant-massless acceleration (leaving solar system) and deceleration (entering solar system), but cannot power any other maneuvers.

(But of course auxiliary drives of a different type could)

As I understand it, that's because the field is spherical. If you place a sphere in a river it can only go straight downstream. However if you combine two or more spheres in a line and angle that line with respect to the flow, it's possible to move diagonally downstream to reach either shore.

True, but the magnitude of any locally-tangential component to a spacecraft would be relative to the angular difference in the spheres' locations, relative to the nearest star. No?

Which is to say, impractical for any substantial radius from the solar system's center.

Right, it wouldn't exactly turn on a dime. :D Still, being able to turn at all dramatically increases the usefulness of the drive.