Just my two bits.
It depends on where you filed the original 485 petition. If it was with the local INS office, go right ahead and apply for the extension.
Otherwise, if it was directly with VSC, suggest that you send the EAD extension application to INS, VSC, St.Albans, VT 05479.
If you go to your local INS office, they will have to request your file and the renewal can take upto 90 days (meanwhile you will be out of turn at VSC).
Take a chance!!!!
Good Luck.
BTW, I ain't no lawyer. Just giving you the info that was told to me when I went to the local office to renew my application (Incidentally, I had my attorney applying to VSC directly). Suggest that you check with your lawyer before jumping into any decision.