Yes, it's possible, but I'd have to make a recess in the barrel for the upper leg of the spring, and the wrist would have to step down a great deal so as not to be so big an average hand could not hold it. Hanging on to one of these is VERY important because they could really hurt you if they come out of your hands. If the hand can't close at least 75%, the gun will jump out no matter how hard you try to hold on.
I could also make a recessed breach plug, but that still presents a problem with a forward mounted spring. I have one designed for a 2 bore gun that I may make in the future which used a long stirrup to link the spring with the tumbler, so the lock plate is low enough to bring the spring under the curve of the barrel. However, no matter what is done, it's always a metal working project to make a lock to fit such a large barrel. There is no easy way.