I am assuming you are replacing the entire cable (inner and outer) so it will be a pretty simple job. However, if you have no mechanical skills (or tools), you probably are doomed to the dealer.
If any of you guys are interested, I have about 4 sets of these which I never used on my Triumph Speed Triple/Speed Four back in 2004/2005. They will probably fit the BMW OK. Get me here or sshards@paradise.net.nz if you're interested and we'll discuss sizes/prices etc.