I can only theorize about how you would attempt to trace someone's IP. I want to know the opinions of people more knowledgable about the subject.
It's the same as in Bitcoin. You have to connect to a large amount of nodes, and see which node you first heat about that tx first. Then this node is either the originator, or "closer" to the originator than the ohter nodes you're connected to. "closer" here means closer in relay time, wihch depends on internet connection speeds, etc.