I thought that exact same issue would be a problem too Umpa, but the chain is so slack, it's almost touching the road!! I've made it clear to the guy who's offered to have a go that it mustn't be made so that the tensioner is unemployed. I stressed that if he had to take a link or two out, that it must be done so that the tensioner still has something to do.
You're probably right, it may not be a genuine C5 chain at all, but then, I really don't know a C5 chain from any other. It may even be a 'bodged' chain from some other source, but one thing's for sure, and that is that surely it can't go on being so long that it hangs so far that the tensioner spikes are miles away from the chain?
If it doesn't work, I'll ask him to re-fit the links, and see if I can get the local bike shop to take a look.