The bonus miles promos may not post in time to save you. You may want to look on theCoupon Connection board and find a FTer who is willing to trade for a 500-mile Delta certificate, such as the ones that are issued through Greenpoints. Those generally post fairly quickly (and I assume would buy you the extra 3 years), and a nice letter to go along with it surely would not hurt.
You might also try opening a Clickmiles account and making a small purchase. They usually have something available for a decent bonus (e.g. PlanetRx purchase for 500 miles), which posts almost immediately, then transfer the ClickMiles to Delta.
[This message has been edited by cactuspete (edited 12-19-2000).]