Many of the tools in SolidWorks can be used for purposes outside their original intended use. Did you know that Weldments can be used for wooden projects as well?
You can customize your Weldment profiles to include common wood cross sections, including 3 X 4. 3D Content Central includes samples of these types of profiles (access 3D Content Central via the SolidWorks task pane under Design library, or 3D Content Central).