I dont think its possible - could be wrong though. I've had a similar issue, and ended up creating one Crystal Report with 40 instances. Took ages to setup, but once it was done, I never had to worry about it again...
The functionality you require is called report bursting. Google "Crystal Report Bursting" and you'll see lots of advice from SAP (and others) explaining what this is.
I haven't set this up myself but I believe that this requires an additional licence for additional Crystal Server modules to get this ability. You can check this by running CMC (Central Management Console) on your Crystal Server box from the Crystal Server 2008 group. Go to a folder and click Manage - New. If you don't see the option to create a new Publication then I believe that the functionality isn't enabled on your licence currently.