Unfortunately thier is nothing in COM which can help you in attaching a content database to a web application and then to create a sitecollection on it.
You can use admin.asmx webservice alternatively which would be available under central admin webapplication
http://CAURL/_vti_adm/admin.asmx
This can help you in creating sitecollection but i don't see OOTB service to create Content database for that you would have to create your custom web service