There is a write-up on the Xoutpost from someone installing E46 sport seats in his E53 X5. Just some minor plastic parts to transfer from what I recall.

If you have E60 seats, this might work. You have some basic things to check:

a) Will they bolt up (bolt pattern for seat real / floor ban). Inspect, measure and check.
b) Do the E60 seats have a provision for the seat belt anchor (look at the outboard rear of each seat, you'll see how it attaches on an E53 seat).
c) Will they connect (electrically). Look to see if your E60 seats have the yellow multiconnector, ideally UNDER the seat as on an E53.
D) Space in the car (no interference with the console, door, dash, etc.). You know once you install them (assuming checks a, b & c give you the green light).

Overall time would be all of an hour or so if you're lucky. Two bolts, two nuts, one connector per seat. Leave the ignition key in your pocket so you don't have a airbag or similar warning light.