If they wont allow data to leave the site then you need to look at an option such as platespin powerrecon which requires installing locally on a windows system.
Have you tried showing the customer the security guide for CP - you can mask server names if you need to.
If you can't deploy a tool at all then you need to utilise the metrics gathered manually - and unless these servers are performing some high computing requirements then they should all consolidate to a suitably sized single host - or 2 for resilience and redundancy.
Matt, you may want to also have a look at the Lanamark Suite Services Edition. It provides you with the best of both worlds - uploading the data as a convenience feature or disabling it and having all the data stored locally.