Backdating IP Groups

I have just added a new IP group with an IP range in it for a couple of interfaces on a couple of routers. It is starting to collect data fine. However, what I need is an option to tell Netflow to use all the data that I have already (raw data) to backdate this IP Group information. One thing that always seems to happen is that I am asked to see what a particular IP address or site was doing (in the past). Obviously I have the raw data but using troubleshooting is so slow. Every time I change what I want to see it takes 15 minutes to generate the next report. It would be better to have a one off long period where it assembled all the data together but which would then mean I could switch between all the different reports much more quickly.