Could'nt one of the custom barrel makers make something for you or them to silver soder or braze onto the barrel to make it legal?
Or on secont thought how about tradeing the barrel in to Ed for a 16" ( or longer) barrel in the caliber of your choice. I know I traded a hunter 17.4" 45/70 barrel plus some boot for a 6.5" 9mm barrel. Worked out great for both of us. Might be a way to solve your problem.