Use VWS API to add user created Markers to DB?

Hi there. I am developing a mixed reality game. Currently I am using precreated image targets and vuforia works reasonably well for the application. However I would want users to use their own markers and simply assign my content to it. E.g. scan paper magazines, boxes etc., add the dimensions, crop and skew with a simple android app. Without this possibility I might need to switch to ARToolkit (I want to avoid this). Is it possible to create targets locally on the device? It seems that the VWS will only work with the developer authorization key.