I don't think an internet coffee is the best idea really. The usually have cameras recording. So, your face will be recorded for Sony to see.
The open wifi alternative is much better. Just drive a couple of miles away from where you live and use any wifi that you can connect from inside your vehicle. You can change your mac address or buy a wifi dongle and then dispose it. As you wish. Use a tor network with a couple of extra proxies of your choice just to be sure (in case tor was compromised). Release the info. Drive back home. Restore mac address and delete the evidence if you wish.
It's not that difficult to be completely anonymous these days. If Sony wants to find you it will need to contact every proxy you used in the middle and then track you to the open wifi. Where they will find nobody. Even tracking you down up to the open wifi is almost impossible.