How to change default user (ubuntu) via CloudInit on AWS

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http://serverfault.com – I'm using CloudInit to automate the startup of my instances on AWS. I followed the (scarce) documentation available at http://bazaar.launchpad.net/~cloud-init-dev/cloud-init/trunk/annotate/he... and examples on /usr/share/doc/cloud-init, but still haven't figured out how to change the default username (ubuntu, id:1000). I know I can create a script to manually delete the default ubuntu and add my user, but seems counter intuitive given that CloudInit exist exactly to automate the initial setup. Any ideas? (HowTos)