Sync-Gateway user accounts built in Couchbase Server

I was wondering if there is a way to build a user account on a Couchbase Server using the Java SDK and then through bucket shadowing have the user account be turned into the proper Sync-Gateway User Data format(with the all_channels data built, and other synching metadata fields).

Currently the only way I see to create a synch user is to use the HTTP REST API from the client app, but I need to build my users from a web app and have them replicated to the sync-gateway bucket. This way when the mobile app is ran the users will not have to create accounts and will be able to use the data they have already set up.