I've actually tried to do so, but as the PrepareMessage() requires, I have to load the delivery first using "NLWS.nmsdelivery.load(XXX)" and as you know both PrepareMessage and load are Javascript fucntions, which I'm currently enable to pass inside the soap envelop (I can't find a way to insert Javascript code inside SOAP XML under the entity tag).
If you could give me an example on how the call is executed, It would be much appreciated.