...well, in advance of the lottery actually running, we can perhaps all agree that it is a good idea to give the selectees drugs that will induce extra courage, and shoot them if they run away.

I've set my line of retreat at a much higher extreme. I expect humans trained in rationality, when faced with a situation where they must abandon their rationality in order to win, to abandon their rationality. If the most effective way to produce a winning army is to irreversibly alter the brains of soldiers to become barbarians, the pre-lottery agreement, for me, would include that process (say brain washing, drugging and computer implants), as well as appropriate ways to pacify the army once the war has been completed.

I expect a rational society, when faced with the inevitability of war, would pick the most efficient way to pound the enemy into dust, and go as far as this, if required.

Caveats: I don't actually expect anything this extreme would be required for winning most wars. I have a nagging doubt, that it may not be possible to form a society of humans which is at the same time both rational, and willing to go to such an extreme.