Right, they are definitely faulty then - like I say when they get warm, they don't extend (apart from the one 2mm) but they actually get easier to push in/out.
The only manual cable I had was a bonnet release from a 940 B230FB. I tried to mount it several different ways. I think I finally found some way to mount it successfully, but on trying to activate it, all I did was pull the lever off the end of the cable in the car - that's the point I gave up (and said a few choice words).
I did find this yesterday though:
http://seekpart24.com/bosch/thermost...ent-1467202302
Over half the price of getting one from Volvo, and that's taking into account postage to UK. Sounds bit odd to me, but for that price I'll give it a go...