Run post-processors with skip_create_ami?

It looks like the post-processors do not run when I use skip_create_ami for the amazon-ebs builder. My goal is to launch a EC2 instance, grab some packages, and download the resulting file and use it as the input to artifice post-processor. But the processor never runs unless I also create the AMI (which I do not need to do.

Is this a bug? Any way to run the post-processors without creating the AMI?