Well, it would be fairly easy to duplicate kdlandis' second suggestion . . . There is an option to duplicate Lesson Plans. Click on the desired Lesson Plan in your list, and then select "Duplicate" from the drop-down menu in the top right hand corner. You can name the duplicated Lesson Plan something similar, with a "Round 2" or something to distinguish it from the first one.
I hear what you are saying though, about having a way to project lessons outside of the normal school year and make it easier to adjust. That is something we can work on.