I'm glad you've got something in mind, I've spent a couple hours trying to find out what the fix novacoin implemented was, even digging through the code, but I can't isolate a single POS fix - there have been quite a few tweaks to POS in Novacoin. I can see that they currently have adjacent POS blocks, so what did they do to address this issue?
AFAIK Novacoin "fixed" this by having a centralized checkpointing system in-place. Essentially one person controlling the whole network (deciding on the valid chain), which defeats the decentralized nature of cryptocoins.