How about this?
The Enterprise is sent to investigate the explosion of the Veridian star. On the way there they encounter a strange energy ribbon in space. Kirk, Spock, and McCoy take a shuttle to get a closer look and when the shuttle starts to break up, they try to beam out only to be sucked into the Nexus. There they encounter Kirk Prime's "echo" chopping wood, and he tells them about an officer from the future who talked him into leaving the Nexus to apprehend a galactic criminal.
They leave Echo Kirk with his Ktarian eggs. The Big Three then travel to Veridian III, where they witness Picard defeating Soran, and just in the nick of time, save Kirk Prime from being crushed by the bridge.
Time for Shatner to say good-bye to Star Trek
: we don't need any more cameos from the original cast.