Maybe you could try re-negotiating the peace treaty. If you're more powerful it might work to make them give something. But you probably won't have their vote on the UN anymore if you do it to often
When I discovered industrialization I noticed a Roman city with 2 coal deposits near my border (I was the first to discover the tech). I tried buying it, even giving them 2 other cities. They still refused. I would take it by force, but then I remembered you can re-negotiate the peacy treaty. Then I could buy the city for 1000 gold and some old tech almost everyone else had. I could have gotten it cheaper, but I wanted to keep the reputation loss to a minimum. War would have cost me a lot more.