I'm breaking your points down into simple logical statements of argument. My point regarding the Ainu was specific to your comment about them being uninhabited, not that they would support the Japanese nor would that fact make the Japanese argument more legitimate -- it is just a comment with regards to the series of arguments or thought processes resulting in the current unpleasantness. The thought pattern goes something like this (albeit not entirely logical):
-Does Japan have rights to the island? Treaty-wise, yes.
-Does Russia have rights to the island? "To the Victors, go the Spoils"
Is the above logic consistent with the state of the world that is being encouraged by the U.S., NATO and the UN? Yes or no? No.
Is there a way we can get around legitimizing "war spoils" as developed nations do not want to encourage that sort of behavior from current developing or rising nations? 1) Say the population now is clearly Russian and 2) Say the island was uninhabited previously.
Are points 1) and 2) true? Yes and no. Population migration or deportation is clearly not the answer. The Ainu existed before either nation settled the land. Situation is complex but a compromise could likely be reached at the negotiating table.
Negotiations? Not agreed to. Show of strength/weakness required? Maybe. Are they on equal footing with regards to military capability? No. Need 'nukes? Maybe.
It's not a good train of thought my friend..