11.4.0 : best storage for large data-sets

The only issue with going the sideband connection route would be that you would have to write the service that the sideband connection calls. The most easy probably is to implement it as a HTTP request as there are already samples floating around to show how to issue a HTTP GET from a sideband call. You'll just have to have an app server routable that contains the service for the lookup. That will probably be the best performing but, as Jason said, an external data group with the "class" command should work for you as well.