You won't find any no-cost conversions, nor no-cost-keep-alive options. This is LH and, well, the market tolerates their behavior.
Their miles' value can be debated heavily, but I'd personally say it's about a penny a mile, so $25 for the Sep expirations. For that small amount of miles, I'd let them waste away; with Lufthansa (especially considering their taxes and fees), I think you'll spend well more keeping them alive than they're worth.