How to let give an IAM role access to read and write from an Elasticache Cluster

Question

I have an ElastiCache memcached cluster. I know how to allow access to a security group, so it can access the cache. However, I wish to allow such an access to an IAM role. Specifically I'm running an ElasticMapReduce job, and I want to allow the task nodes to access the cache, using the EC2_DEFAULT_ROLE IAM role.

How do I do that?