It would be nice to have control over the crop position. The variables mentioned in the title are currently set to zero (near line 167). A quick and dirty fix would be to replace these 4 lines with the following:

sourceX = options.sourceX ? options.sourceX : 0,
sourceY = options.sourceY ? options.sourceY : 0,
destX = options.destX ? options.destX : 0,
destY = options.destY ? options.destY : 0,