@Override
protected ConnectionProvider selectConnectionProvider(String tenantIdentifier) {

if( "xml1".equals(tenantIdentifier) )
    return xml1;

if( "xml2".equals(tenantIdentifier) )
    return xml2;

return null;
}

MultiTenantConnectionProvider multiTenantConnectionProvider =
( (SessionFactoryImplementor) sessionFactory )
        .getServiceRegistry()
        .getService( MultiTenantConnectionProvider.class );
YourMultiTenantConnectionProviderImpl yourMultiTenantConnectionProvider = (YourMultiTenantConnectionProviderImpl) multiTenantConnectionProvider;
yourMultiTenantConnectionProvider.registerTenant( ... );
...
yourMultiTenantConnectionProvider.deregisterTenant( ... );