Unfortunately, no, there is no built-in way to do this.
You'll need to loop through all your toolbars and dockable widgets and write their positions (and possibly their visibility) to a file. To restore, you can read that file and set your positions based on what you read.
The good news is that once you have such a system set up, making a default layout is easy - move all your widgets where you want them, then save your layout file, just like you do the user layouts above. You can even have multiple layouts, as long as they all get separate files.