The easiest way should be to use a unique name for each OBJ file. Therefore, in the [font=courier new]Home.xml[/font] file, you could easily replace each [font=courier new]xxx/objectName.obj[/font] by an URL similar to [font=courier new]jar:http://server/path/object.zip!/objectName.obj[/font].
It's more or less what is done in the Export action of the Exported homes manager that tries to reduce the size of each sh3d file exported on sweethome3d.com, by referencing URLs to free models as often as possible.