with 'offline CDR meditation' you can do a daily measurement with traffic flow.
Log the traffic, list the prefixes on your and their side, calculate the SUM for those prefixes.
I think, a script what running daily can do this job withing 5 minutes.
Another possiblity to manually extend the logged traffic flow with the ASNs fetched from Maxmind (or yours) hash table.
What were you trying to accomplish there that can't just be done with NetFlow into a standard NetFlow collector, aside from the ASN business? IPs -> ASNs that aren't collected from your ASN's perspective can be worthless. There are many situations where this data is different or not complete.