I would say that you should contact the EFF as they are already awayre of this suit and have openly stated that LIGATT has no case. This is one that EFF may take on its own, pro bono to Yahoo users who find themselves with a subpoena.
Here is what you need to do.
(1). get a copy of the subpoena from Yahoo. They should tell you in the email how to do that.
(3). Provide links/copies to the 2 posts of yours mentioned in the lawsuit.
In the email tell her you would like the help of the EFF with this matter and ask her for her assistance. I believe the EFF will help you in this instance and they will likely take the case in house. Good luck and let me know what they say. Other Yahoo users have also, likely received subpoenas. Yahoo has a policy not to release info on any named poster until completion of any motions against the subpoena.
It will be quashed and Greg will have no choice but to withdraw the lawsuit entirely.