A spare DME relay is nice but as an "emergency piece" I keep a DME jumper in the car. Because it is simply 3 connectors hooked together with wire you can visually see that it is correct and with any DME relay you would always have a question what is happening inside the box.
You just crimp some wire between three .157" male bullet connectors. Dirt cheap and pretty impossible to fail. The 3 sockets you need to connect are #30, #87, and #87b.
(I have the numbers on labels on the leads so I don't have to remember.)
MAKE SURE YOU PULL THE JUMPER WHEN YOU TURN THE CAR OFF!