You can write a custom action that can move the doc for you based off a field on the form.
The idea is to create a custom action "save and move" action. Your custom action would have the first action Save and the second a custom code that would move the doc.
Please check the documentation for more details an also check this forum where I answered some questions from customer on this topic (see the search link below)
Also please note that we provide a fully functional code that would give you the right start (see the Sample Code under the product installation server).
If you have any questions or you get stuck just let me know.