I hate being chain stunned as much as the next guy - but I think I've got a solution that is both practical, and 'makes sense'.
If a Demigod is stunned while stunned, it becomes unstunned.
Ie, if you are stunned by a rock from a Rook, and then stunned by TB before the Rook stun wears off, you become unstunned, or in other words, 'you wake up'. 
Therefor, if you want to chain stun a Demigod, you need to time it more accurately, and wait for your target to become unstunned - this will give the victim more chance to escape, because the stun cooldowns will be out of sync.