You can call packery.reload() or just use the packery initialization function again after you have append the images and to calculate every new image position. I use the masonry plugin and masonry.reload().
Update: To make masonry work with infinitescroll use a callback function: How to enable infinite scrolling with masonry?
Here is the code from my website. I use jquery templates and prepend. You can see that it call masonry('reload') after the prepend. It also init masonry from the new container. It also correct the width and the height of each image because I think there is an error in masonry. I think it's not really what you need because I don't cache the brick but I rebuild the entire container when I need it to show a new category. In your example you physically add a brick but I don't understand why it didn't work. The result is the same but not so clean.
$j.getJSON($j("#tag") function(response)
{
// Start masonry animated
if (response && response.length)
{
var container = $j('#container');
container.masonry({
itemSelector: '.brick',
columnWidth: brick_width,
isAnimated: !Modernizr.csstransitions
});
boxCount = response.length;
counter = 0;
$j.each(response, function(idx, ele)
{
container.prepend($j("#brickTemplate").tmpl(ele)).masonry('reload');
}
container.imagesLoaded(function()
{
$j("#brick").each(function()
{
var content = $j(this).find(">div");
var height = $j(this).find("img").attr("height");
if ( height == undefined )
{
content.css({
height: "300px"
});
} else {
content.css({
height: height
});
}
// bricks fade in
$j(this).delay(Math.floor(Math.random() * 1600)).fadeIn('slow');
// Bind Mousemove
$j(this).mousemove(function()
{
.....
}
}
}
}