AWS Cloudwatch getMetricsStatistics Multi-Account programatic Access

I am trying to grab Cloudwatch metrics from multiple accounts programmatically. I have created a master account which the other accounts would provide cloudwatch read only permission to. I did this by creating a IAM user in the master account then created a IAM role that gave this IAM user access to cloudwatch read only. I then try using the Java Cloudwatch API GetMetricStatistics to grab metrics back but it doesn't provide all the metrics from the other accounts. Only the master account's own metric. Is what I am trying to do possible?

Thanks