Your lease assumption rate is very high. But your sales price is actually pretty good.
Why don’t you just sell it to a BMW dealer? Your stated payoff is $59,500 and MMR is currently $65,700. You should be able to get the $5k you’re seeking and it’s a much simpler transaction. You could have the check in your pocket this afternoon.
CPO is given high value in the used market. Rusnak has one with fewer miles sitting at 72k CPO, and one @ Riverside at 69k. There are package differences, and I didn’t spend a ton of time, but there isn’t a ton of skin in it for dealers at OP’s price point with CPO and prep costs, and many of the ones on car gurus have sat for a bit.
So yes, OP may be discounted relative to the dealer market, but many people want that unlimited mileage on the CPO.
I have a feeling your and @nyclife comments may be rhetorical tho. 
PM’d you for the car, located in oc