Has anyone replaced the bonnet release cable on Superb 2, the long cable disappears into the inner wing and appears at the lever in the footwell. Managed to remove old cable but cant even see where to route the new one.

You should of taped the new one to old one with tape and removed and replaced

hindsight  ---   wonderfull!!

Tried taping new cable to old but was so hard to pull through, old cable snapped. Suspect there's a grommet on the bulkhead it passes through. Looks like you would have to remove dashboard to even see where cable comes through!

I replaced a clutch cable on a 306 cabrio last week when the owner tried to do it himself he had just ripped  the old one out 

I had to use an wifi endoscope for my android phone to get up beyond the dash to see where it went through then used thin metal rod to get to hole then taped cable to rod and pulled through

If I didnt have endoscope there would be no way to find where the access was with out it

You can get them quite cheep from Ebay endoscope