We spoke to Motability about this at our last renewal and due to some special circumstances they were very willing to let us buy off list. However, there is a catch. We would have to pay the full difference between the price cap and the trade value of the car ie no Motability discount as the AP. Turned out that was way too much so we kept the XC60 for another two years. If you want to do this you have to get to management level as all you get from the call handlers is its not possible.
The lease is now up in October so the hunt is on!