For TimeSeries API you will have only such parameters like in documentation:
I don't see any parameter that allow you to split results. Maybe it will be easiet to get those metrics directly from cloudwatch?
As far as I understand, you are trying to use AWS EC2 CPU usage metric across multiple entities and group it by AWS region. This metric in expressed in %, so I would be careful with aggregation.
The idea to use tags seems to be a valid approach.
Technical Product Manager