Who says you need to win? You just need to ensure you don't get a 3rd game, which, in the OP's case, should be extremely easy to control, be it losing both or winning both. He clearly stated from the beginning that teams in his league can't demote.
This presupposes that the loss of season ticket holders due to demotion is not assessed, which I don't know to be the case (or not to be the case). If it's treated as a team demoting, and then autopromoting due to bot promotion, the STH loss is not offset with a corresponding gain, and that'd be significantly detrimental to future revenues. I might have to actually check that next season if I can manage to lose enough games in IV, though I won't be going out of my way to do so. ;)