Currently there is no way to do this properly directly from Vectorworks. The best method we have found so far:

1)       Export from the Design Layer(s) to STL, this gives you a 1:1 scale model by default.
2)       Bring the STL into your slicing application, or into MeshLab or NetFABB Basic, two free application that allow model scaling.
3)       Scale the model to the desired size.
4)       Save/Export the STL after scaling.
5)       Print

If you try to manually scale down the objects in Vectorworks, plugin objects like doors and windows will no longer appear or function properly. The only way around this is to break apart the plug in objects which then renders them unusable. Scaling the STL after export keeps your file functional as well as allows perfect scaling without doing so manually objects by object.