Wide neck adjustment

Hi there! My partner is a perfect size Large, except for his neck which needs the collar lengthened by at least two inches. Does anyone have any suggestions as to how to make this happen? I'm fairly confident I can grade up the collar/stand pieces themselves, but where else do I adjust the pattern? If I add an inch to both of the center front seams, I'll be adding extra room he doesn't need in the torso, and lowering the neckline would mean the collar might sit too low on him. Any advice would be much appreciated! cheers, v