If you are looking for a command that will completely automate your task it isn't in autocad (at least not that I know of). You didn't state how you do the bridging now, but I think the command you want is 'BOUNDARY'. See the attached drawing, you will need to arrange your parts manually shown in red then drop in bridging rectangles shown yellow, your base line shown blue, and finally another rectangle to surround the whole lot (you could use the size of your sheet material for that to make sure it all fits) then issue the BOUNDARY command and pick any point outside your parts but inside the outer rectangle as shown and the polyline shown to the right will be created for you (I moved it to the right). You just need to make sure there are no breaks in your geometry.