I would recommend building up the front, You could probably insert a piece of 1x1 or 2x1 inside the front edge of cabinet, put the same on the front bottom edge of the cp panel. The hardest bit will be working out the angles you want where those 2 pieces sit. An electric planer would make the job a quick one, But a hand plane could be used just as easily.
Once that is done you will need to make 2 small patches for the sides, 1 for the front. Adjust the angle of the back of the CP to account for front adjustment.