You will need the blocking tasks to intercept the creation events.
the instantiateVapp is likely to be the item you need to intercept.
you will need erlang and rabbitmq
This site shows how to install on a windows box
http://cloud.dzone.com/articles/how-setup-rabbitmq-amqp-vcloud
This page shows how to setup the blocking task.
http://blogs.vmware.com/orchestrator/tag/blocking-task
The trick to blocking tasks is understanding routing keys, there is a package from the vco group called notifications which assists with the configuration of blocking tasks. Not sure of the site sorry but you can't find it email me direct and i will send to you.