Sorry, I don't know --- haven't looked for it for several years. When I first joined EC, it didn't look too clear to me, so I called and was told that there's no charge for spouse or business associates for EC members.
I've had a free EC membership for ~ 8 years, and DH always drives. We use National 1-2 x/year at Disney. When we leave, he hands the person my card, his license, the coupon and the confirmation. And then we're off. There's never been any discussion.