If you can't find anyone who can give you a test drive, another option would be to go with a local car club and do a self service rental of an EV for as long as you need to test it out. Especially if you add a promo code you could get a good discount on that too.
Not going to be free, but it gives you as much time as you want and no pressure from sales people when you return it.
Where abouts are you, and what model are you looking to try out? I'll see what I can find.
(if you're nowhere near MK, traveling to the experience centre to collect a car for a week isn't a great option either. I believe they have a fairly small mileage allowance and charge a fair bit for going over)