Does anyone know, if it is possible to make osm2po able to load extra road data into SQL file, such as the surface tag?  I know it is not much used, but when it is, it would be nice to know if the surface is solid or soft.
I am able to set a category by using tags, .e.g., wtr.tag.surface.gravel, but then I can only set it to another category. It would be nice if I could pass on both the category and the surface :)
Any good ideas?