For each month all broadband filters (Z,Y,J,H,K) have associated correction tables and overview plots presented. These are based on the most recent calibration that uses individual detector magnitude zero-points (also computed monthly).
The coordinates used in both tables and plots are standard coordinates (units are degrees) with respect to the tangent point of the telescope optical axis for that pointing (see for example Smartt "Spherical Astronomy"), rather than detector pixel coordinates.
To apply the corrections we suggest using something like bilinear interpolation to compute the offset at an arbitrary detector coordinate. The correction is derived from the "average" difference between the local magnitude zero-point of 2MASS stars and the detector magnitude zero-point and therefore is applied additively.
We caution that since this is derived directly from 2MASS stars ie. relatively bright stellar objects it may not be directly applicable to faint stellar objects or non-stellar sources.
All the illumination correction tables are available from here.