Get per-core CPU load in shell script

I need to report the CPU load per core as a percentage from a shell script, but **I cannot run e.g. mpstat for one second**. Basically I think that the infos top is showing after pressing 1 is what I want, but I cannot configure top to show this in batch mode (at least I don't know how). I could create a ~/.toprc file with the configuration, but then I have to hope that the users do not mess with it. I looked at mpstat and parse the output, but this supports only seconds as interval time. My script gets called via SNMP and waiting 1s for the response will generate a timeout, so this is not an option. Are there other ways to get the per-core cpu load? I read about parsing /proc/stat, but I think this is more a last resort.