Unfortunately we do not support running a job in EC2 that can leverage GPU yet. we are working on that support now and you should be able to use that in future release. We will also consider the requirement of being able to launch GPU EC2 instance from non-GPU GraphLab Create client.
For now, the way you may leverage the GPU is to launch an EC2 instance yourself, ssh to the machine, install appropriate driver and GraphLab Create GPU version there. Check out the following notebook for example regarding how to leverage GPU for training a neural network:
Hope this helps and please let us know if you have additional information.