By the way, I know this must be possible as I used to work for a company that used a product (relatively expensive, I might add) called "WebTrends for firewalls & VPN's" that would do exactly what I would like to do.
It is trivial to produce a number and claim it means something.
It is much harder to produce a number that really means what you have claimed.
The fact that a proprietary product claims to accomplish a goal is not always very good evidence that that goal is, in fact, technically accomplishable.