I created a similar script, mine is completely controlled VIA groovy though and it has a UI and works rather well. I posted the code here and commented the majority of the code decently well. Feel free to edit, use or copy what you need. I don't have access to my work computer right now so I can not be of too much more assistance.
http://forum.soapui.org/viewtopic.php?f=5&t=22445&sid=a3fb892aa2e9054c57b6e91bbffe9348Feel free to ask for help with the code anywhere you may need it if you choose to use it. Currently it uses a property file style for the inputs and tags within the xml like [property] where property would be what's found as the key in the property file (Ex. FirstName = Paul would replace [FirstName] with Paul).
