Updating PSTCollectionView contents while loading photos

Question

I'm using PSTCollectionView class to load the photos from iPhone camera roll. I want the photos to appear while they're loaded though, not wait until everything is read. My code looks like this:

-(void) loadAssetGroups {

        void (^assetGroupEnumerator)
        (ALAssetsGroup *, BOOL *) = ^(ALAssetsGroup *group, BOOL *stop) {
            NSLog(@"group....%@",[group valueForProperty:ALAssetsGroupPropertyName]);
            [self loadAssetForGroup:group];
            }
        };

        void (^assetGroupEnumberatorFailure)(NSError *) = ^(NSError *error) {
            NSLog(@"A problem occured. Error: %@", error.localizedDescription);
        };

        [[ImagePickerViewController defaultAssetsLibrary] enumerateGroupsWithTypes:ALAssetsGroupAll
                                     usingBlock:assetGroupEnumerator
                                   failureBlock:assetGroupEnumberatorFailure];


}

-(void) loadAssetForGroup:(ALAssetsGroup*)group {
    ALAssetsFilter *filter = [ALAssetsFilter allPhotos];
    [group setAssetsFilter:filter];
    __block NSMutableArray *indexes = [NSMutableArray arrayWithCapacity:0];

    [group enumerateAssetsWithOptions:NSEnumerationReverse usingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
        if (result == nil)
        {
            return;
        }

        if (![self.allPhotos containsObject:result]) {

            [self.assets setValue:result forKey:[result valueForProperty:ALAssetPropertyURLs]];

            [self.allPhotos addObject:result];

            [indexes addObject:[NSIndexPath indexPathForItem:[self.allPhotos count]-1 inSection:0]];
            [self.collectionView performSelectorOnMainThread:@selector(insertItemsAtIndexPaths:) withObject:[NSArray arrayWithObject:[NSIndexPath indexPathForItem:self.allPhotos.count-1 inSection:0]] waitUntilDone:NO];
        }

    }];
}

From the console I see that collectionView is calling its dataSource method cellForItemAtIndexPath for the first few objects (that would be visible on the screen) but I need to wait for all photos to be read until I see the collectionView refreshed.

Is there a way to have it running more "on the go"?