Well, here is a crazy suggestion: If the barrel is reasonably short (i.e., 42" or less) you could mimic a rifle that was cut down at the muzzle for one reason or another. The KRA CD showing Kentucky-made longrifles has a Rizer and Weller rifle that was obviously cut down in this way - nosecap was set back and the ramrod groove was just faired down to match, with no attempt to rework the molding. The molding just runs right up to the nosecap inlet.
You could glue a piece of wood to the end, fit a muzzlecap long enough to cover the joint, and round over the end of the ramrod groove. Then you drill a hole or two in the forend, with inlets to match, where the thimbles were before being relocated, and presto! You have a rifle that was shortened for use on horseback.