Hi,
Is there a way to pass data/payload (say key value pairs) to the vcloud VMs ?
Not sure if this is what you nee or not, but take a look at custom data attributes via ovf.
http://blogs.vmware.com/vsphere/2012/06/leveraging-vapp-vm-custom-properties-in-vcloud-director.html
I prefer to use object metadata as most vCD objects have metadata options.
then its just
object.metadata.enumerate()
check out the VclMap types api