Clutch cable length will be determined by the style handlebars mounted- either the low Euro bars or the dealer-installed 'western' bars favored by many NA buyers. What style bars do you have?
As to routing, the clutch cable runs down the front downtube on the right-side of the chassis. At the lower bend on the frame, a zip tie is used to secure the cable. Not overly tight.
Part #32 73 1237694 is for the 1495mm length clutch cable. Easy to confirm the correct part
after you determine what handlebars are mounted. If unsure, a quick call to Bob's BMW will get you squared away. Or your local SA dealer.
http://www.bobsbmw.com/ for parts fiche.
I would also suggest you confirm the correct position of the clutch lever located at the aft end of the transmission. I kinda doubt a BMW braided cable could stretch to the point of being unusable before it broke. Also, confirm the cable's required barrel is still installed in the clutch lever. Without the barrel, the length will possibly trick you. A forum member just recently discovered his bike was laking this vital, little part.
Report back with your findings.