Not saying that the following would work, but simply as a seed to open up discussion a bit:
"Gaku, I [and name(s)] are going off to find the Otter Scroll because apparently all the other Leaf clans are too damn lazy and we're not going to sit on this even if they do. The research I've done says that the area is fairly safe, but just in case something bad happens and [I / we] don't make it back, here is a document defining the Gōketsu line of succession and a series of 'final message' letters for various friends and family members. Those letters should be sent ONLY if I'm declared dead. Seriously, some of the contents are embarrassing so do not send them unless you're sure I'm not coming back, okay?"
~some months later~
"Lord Nara, this is the 'final message' letter from Lord Gōketsu to you. He suggested that the contents might be embarrassing, so it might be wise to open it in private."
~Shikamaru goes to a private room and opens the letter~
Dear Shikamaru: Well, looks like I bit it. Guess I got too cocky, huh? Without me [and <names of people who went with>] I'm not convinced that the Gōketsu will survive, so I'd like to offer you a deal: adopt all of my civilians now and all of my ninja as quickly as you can, prioritizing the ninja over any other potential adoptees. In exchange, here is a sealed envelope containing all the Gōketsu shinies; if you agree to adopt everyone then go ahead and open the envelope and get the shinies. If you don't agree, please burn the envelope. Obviously I can't enforce this deal from beyond the grave but I'll trust you to be honest. You're a good man and I'm glad to have known you. --Your loving brother-in-law, Hazō