A couple of candidates for an enhancement to the trace image dialog would be:Place tracing image on chosen plane, don't worry about location. OK the image. Select 2D sketch on the same plane as you placed the image - zoom in to image 'origin' and hover cursor (note the coordinates from status bar at bottom right of window). Exit sketch mode.
Now Edit the tracing image - use the coordinates noted in previous step as the offset values (you'll need to switch sign to get movement in correct direction) -OK the edit. 'Origin of your tracing image is now directly origin of the plane it is placed on.