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)
Most BMW dealers will allow extended test drives in the i3. Sytner Leicester let my wife borrow one for 4 days. Allowed her to try the car in every day life, commuting etc. That was 2016. Ordered one as a result.
When her i3 was in for servicing Sycamore Peterborough kindly arranged for an i3S to be her loan car for 3 days. They went to the extent of tracking one down from BMW UK and having it delivered just for her to use.
Bought one as a result.
If you demonstrate to the dealer that you’re genuinely in the market, but need to try an EV to make sure it fits into your life, they should accommodate. its a big change from the convenience of dragging 600 miles of fuel around behind you.
Despite the other failing of their dealer network, BMW certainly seem to understand that and their policy on test drives has helped them sell a lot of i3s.