Although I am no medical expert, it is a subject I am interested in and I do know a few people with a similar addiction. I must admit to being partial to the 'odd' codeine tab myself!

However, I would suggest that taking 6-8 tablets a day is not too bad, (i know people who take more than double this, and are totally dependent) although given that the back problem has now ceased and there is no more pain, it is clear that this person may be reliant upon them.
Sometimes an addiction to painkillers can start as it is just the fear that the pain may come back if they stop taking them and take them just in case.
I would suggest that this dose of 8 tabs is not desperately worrying, I am presuming that they are 400mg tabs and that just one is taken at 3-4hour intervals? Personally and from experience, I don't think it would be too hard to ween off.
If this person is taking 8 tablets a day, I would reduce the dose by one tablet each day, but I do stress I am not a Doctor! (also it is unclear exactly what doses we are talking about here)
Unless this person has other problems in their life such as depression or severe anxiety, it should not be hard to do. If there are other issues and the codeine is being used as a way to deal with them, well then the other problems need to obviously be delt with.
It is very easy to become addicted to codeine, because of the relaxed and calm feeling it gives, the biggest danger in this situation is that this person will eventually need more and more codeine to get that calm feeling that they may crave, so really it should be addressed now, before it becomes too difficult.