Welcome to the Cove
You defintely have the tiger by the tail and I do not envy you a bit. Without having seen any of your system documentation but having read and re-read what you've said I think you have more of a people than a system issue here, so don't pull it's plug yet.
The task at hand is not impossible, but highly improbable and based upon your own statement the odds of your success are not in your favor.
I'd bet a dollar to a doughnut that the only reason your organization got the certification to begin with was as you say "customer requirement" as as such there was nothing expected to be gained other than maintaining the status-quo and it has resulted in a picture perfect example of "what comes out is equal to what goes in"
My friend until you can figure out some way to effect a change in attitude on behalf of decision makers you could have the best designed and documented system there could possibly be and you'de still wind up in the boat you're in today.
If you really want to try though then you need to start at the very beginning of the information contained in the ISO 14001 Forum here in the Cove and really study it (you'll need to seperate the wheat from the chaff). Listen to the advise the good folks here give. Don't waste money buying those self-help books on the subject because all they say is already in here and it's free. I think someone has already suggested that you get a copy of ISO 14001 and read it (if I had said that the admonishments would have flowed like water down the Nile). I would also recommend that you get a copy of ISO 14004:2004 because it contains very good, relevant information that you might find useful.
All the above aside will be useless unless you get your organization on board and that's what you yourself have to do. A good way is to find some environmental objective or goal that when finished can result in a bankable return on the investment of time and resources. You're going to have to come up with something real and tangible that say's "Hey, it wouldn't have happened if we had not used our EMS."
Good luck...Oh yeah, trust your DNV auditor. I see some of the work those guys and that company does and it's top of the line.