We cannot detect the stack's remaining movement unfortunately, so we have to do it on the general's. As said, it's debatable to disallow anyone to join the games if he's just sticking around in a fleet somewhere (in fact he'd probably have to spend less time to get there than the rest). Currently a general needs to retain at least half his move to be eligible for attending.

Woirble's suggestion might have some merit though. We may consider this for EB2.