<command name="tt_data"/>
You can use simply "tt_data" command as Andy replied. Or you can use FormAPI script to invoke a workflow. For this you have to do little hard work... It depends on your use case. For FormAPI solution you should go through FormAPI and SP_developer guide.-Enjoy
My name is not Andy - and while one could initiate a workflow through FormAPI / callServer scripts there does not appear (from the initial thread) to be any reason for that level of complexity.