[libvirt] Userdata for libvirt?

Hi Experts, Forgive me if not clear enough, will try to be describe what I need. What I need: Start a VM on a remote libvirtd server based on an existing image (Might or might not exist on server), plus some userdata. It is pretty much the same like EC2 or Eucalyptus, but we need to run on our private cluster with only libvirtd. (Eucalyptus doesn't support using physical disk in VMs, that is what we need). I went through the Remote Libvirt control section of the Documentation, but couldn't find a way to pass the userdata to the VM started. Does libvirtd already include such feature of do I need to make my own. Thanks -Yushu