My wife's 765 was pending for more than 90 days and the old one is expiring. Called NSC and the rep told me to fax them a short letter and a short employer letter. I made up both letters with content outlined below.
1. State the reason you are requesting a expedited request and how long it has been pending. Also say you will lose your job without EAD which will result in significant financial losses.
2. A#, Case # and other contact information.
The employer letter in company letter head just states
1. They like you and they will lose a valuable resource if you do not have EAD.
2. Ask them to expedite your application because of it.
I faxed the letters to NSC on Monday evening and today it is approved. (Ironically, our green card was approved on Monday right after I sent the fax, but I think the fax does work to expedite EAD). Hope this information helps for those with expiring EAD.