NSPersistentStoreCoordinator *coordinator = [appDelegate persistentStoreCoordinator];
NSManagedObjectContext *newContext = [[NSManagedObjectContext alloc] init];
[newContext setPersistentStoreCoordinator:coordinator];

[[NSNotificationCenter defaultCenter] addObserver:appDelegate selector:@selector(contextDidSaveFromSeparateThread:) name:NSManagedObjectContextDidSaveNotification object:newContext];

// model work done here

// when this executes the notification fires which should execute contextDidSaveFromSeparateThread: which then merges the contexts
if (![newContext save:&saveError]) {
    NSLog(@"ERROR saving in registerTheUser: %@", saveError);
}

[[NSNotificationCenter defaultCenter] removeObserver:appDelegate name:NSManagedObjectContextDidSaveNotification object:newContext];

[newContext release], newContext = nil;