I know of no support method. If you want to try something and see how it works for you (in test/dev), you may be able to call the vSphere API methods via VCO to do the consolidate operations (promote virtual machine disk), at least on the guide I have here it does not seem to require the VM be shutdown. However I have not tested this and I know vCloud might be a little confused as it does not like things changing in VM's it controls.
However if I was needing to do this I would feel more confortable just coming up with a time (maybe per VM) that I could have the customer shutdown for the time it will take. (Maybe during patch malignance window or something). Might only be worth it on hiher IO system, as not using the delta disk (linked clones) IO operations will be faster.
Wish I had better news, but with the current release I do not see a way to do it, that is supported (or really tested).