I think what you're looking for is the Cloud functionality available in version 15.08 and newer. In your slurm config set the node state to CLOUD and then the nodes will be requested for startup when they are required via the Resume and Suspend scripts.
I have been playing with this myself and have found some limitations in the way that the cloud support is implemented in that it forces you into a particular work flow e.g. there isn't an easy way to make use of spot fleets on AWS as slurm wants to control when the nodes start and stop.
