How can the oblateness of Earth impart torque to change the longitude of ascending node of a satellite?
I'd like to start by quoting from the Wiki page on Nodal Precession you mentioned: 


  A non-rotating body of planetary scale or larger would be pulled by
  gravity into a sphere. Virtually all bodies rotate, however. The
  centrifugal force deforms the body so that it has an equatorial bulge.
  Because of the bulge the gravitational force on the satellite is not
  directly toward the center of the central body, but is offset toward
  the equator. Whichever hemisphere the satellite is in it is
  preferentially pulled slightly toward the equator. This creates a
  torque on the orbit. This torque does not reduce the inclination;
  rather, it causes a torque-induced gyroscopic precession, which causes
  the orbital nodes to drift with time.   


(emphasis mine).  Note that this is a small force and the precession is slow compared with orbital speeds.  Precession towards (or coasting away from) the equator thus is a change in latitude compared with what would be expected, and this "twist" changes the expected longitude at a given point in time because the satellite's vector velocity changes (I believe in both direction and magnitude, but I'm not certain about the magnitude).