I've always thought memory seats are a waste of time, particularly if there is only one main driver of the car - the 640 has them though
Not sure about the legitimacy of taking over a lease, am sure it can be done with the approval of the lease company - BMW finance in my case. There are companies that facilitate lease swaps so presumably it isn't out of the ordinary.
http://www.swap-a-lease.co.uk/index.cfm