Cloudwatch and alerting with variables

I understand that template variables are not supported inside alerting. My dashboard contains a 1000’s of servers for which I monitor CPU usage. So I must use a variable in order to get a list of all running instances, however upon setting up alerting I get " Template variables are not supported in alert queries " - is there a work around I can implement to get alerts when one of the servers is high CPU?

Here is my query I am issuing: