You can't just "funnel a rogue transaction" through someone's node because of the decentralized system. Any transaction sent to that node will be broadcast to the node's peers and thus to everyone. Hence the decentralization.
You could chose to connect to only one bitcoin-node with your bitcoin client. Would not the relayed ip of your tx then point to that ip, or would it point to your own ip? I'm unsure how 'relayed ip' is inserted to the tx, what I do know is that at least one person had their home raided because of their "Relayed by IP" showing up on blockchain.info. That was a mistake, but still not fun for the person in question. I'm sure some others could bring a link to that case, or any interested could google it. AFAIK, it's not confirmed, but I have no reason to distrust that report, as it is actually likely to happen.
Let's say some transaction gets the attention of law enforcement, and since the officer handling the case might not be the brightest bulb, he just goes to blockchain.info and sees the "Relayed by IP" and then gets the home address from the ISP and raids the house. It's possible.
The relayed ip is not a part of the bitcoin transaction. That is simply something displayed by blockchain.info for the node that relayed the transaction to them. This does not point to the node that originated the transaction and the ip addresses are not a part of anything in transactions or the blockchain.