Okay, this requires that you have Chef preinstalled on your AMI:
http://scottwb.com/blog/2012/12/13/provision-and-bootstrap-windows-ec2-instances-with-chef/
But this is a strategy for installing Puppet to a stock Windows AMI, which could easily be modified for Chef:
http://dansrandombits.blogspot.com/2012/06/bootstrapping-custom-windows-ec2.html
I can't say I've done this yet, but I've both in my bookmarks bar since they was posted and have been planning on giving it a shot in at least our dev environment at some point. It seems like as long as there's a solid silent install for Chef, you could pull this off.