Please stop. We've already hashed this out. Shatner's Kirk died in Generations. There's no need to resurrect him not for any reason. Not even for a flashback, or memory. Let it go. Face the facts. William Shatner is an old man who barely has any resemblance to the Kirk we once knew.
Chris Pine is Kirk. Let's allow him to captain this crew. Even Nimoy should step back out of the picture. A mention of Spock Prime and his work with the Vulcan colonization effort is enough. The last generation must give way to the next.
TGElder NCC 1701-E