He may be reluctant to rent an ecv the first day. Might want to politely ask him the 2nd or 3rd day. He may realize there are lots of people in scooters, and its not that bad as he thinks.
He may then reconsider his position.
Another idea would be to offer to share the ecv with him. Let him know he is free to walk part of the time, and you will drive it for him other times, so he can stretch his legs out. Its really not good to be sitting in a wheel chair the whole trip, especially if you still have some mobility. You will loose some leg strength sitting the whole week. We do the push wheel chair. I've got arthiritus and tendinitus in knees, and hips, and no way could I be on my feet 12 hours a day for a week. So, I get up and push the chair, or my husband pushes it and I hobble around sometimes and I ride in the chair at other times. We get some funny looks. But I work hard at the gym on my functionality, and mobility, and training so I don't want to be sedentary for a week. I'm not saying if you need to use the wheel chair 24-7 that you should try to walk. Just that I know there are semi-mobile people in need for mobility assistance.
For myself, my legs feel great the first day. I might even be able to pull off a half day without a wheelchair, but then I'd be dead for a couple of days and sore too. You don't want to be in pain on vacation, you want to be happy and having fun!
Connie