So what you are looking for is a way to build a dynamic form? It is possible to have a form design such that it pulls in a secondary data source (another xml file, etc) and constructs itself based on that. A valid example of this is a survey form. There would be the form that users open to fill out the survey, and the one that the admin uses to create the XML source file for the survey.
It sounds like you want to do something similar to this. It is possible, and has been done before, it just takes careful consideration of design to make it happen.