Featured image on single post as div background.

Something like this might help: http://wordpress.stackexchange.com/questions/115954/featured-image-as-background-image-on-pages

So you could write some CSS in the wp_head hook in GP Hooks like this:

<?php 
$thumb = wp_get_attachment_image_src( get_post_thumbnail_id( get_the_ID() ), 'full' );

if ( $thumb && is_single() ) {
    ?>
    <style>
        .whatever-element {
            background-image: url( $thumb );
        }
    </style>
    <?php
}
?>

Make sure you check the "Execute PHP" checkbox.

Thank you Tom, that did the trick.

At first the code snippet you provided didn't exactly work. With the help of the link you provided, I was able to get it working.

I replaced
background-image: url( $thumb );
with

background-image: url('<?php echo $thumb['0'];?>')

and it worked perfectly.

I also added the following CSS so that the post image is hidden on the single page.

img.wp-post-image {
     display: none;
   }

Ultimately, my final code snippet looks like this:

    <?php 
$thumb = wp_get_attachment_image_src( get_post_thumbnail_id( get_the_ID() ), 'full' );

if ( $thumb && is_single() ) {
    ?>
    <style type="text/css">
        div.page-header-image-single {
            background-image: url('<?php echo $thumb['0'];?> ');
            background-attachment: fixed;
            background-repeat: no-repeat;
            background-position: top;
	    width: 100%;
	    height: 300px;
            margin: 0px;
        }
        img.wp-post-image {
            display: none;
        }
    </style>
    <?php
}
?>

Thank you again for your help. The add-on made it very easy.

Ah, of course - that's what happens when you provide code at midnight :)

Glad you got it sorted out - thanks for posting the code!

Just passing through the comments as I was merely looking for the same thing.
I got your solution working, but there's an extra catch: the image must be blurred.
Came across the same effect on wpclips for genesis: http://clipbank.wpclips.net/clips/genesis-bg-featured-img-fx/ and that's exactly what I was looking for, but for generatepress.
The problem I have is that everything is blurred, except the background image.
I guess a container must be added just after the body?
Could you help me out on this?
Thanks.

Hi there,

I'm not too sure what you mean? Can you show me an example of the blurred image?

Hi Tom, thanks for replying.
I followed the demo on http://demos.wpclips.net/templates/genesis-bg-featured-img-fx/ and found a solution.
Just hook a div for the image in the wp_head, css add the featured image to it, flip and blur.

For those who are looking for something similar, here is the code. Don't forget to execute php.

<?php 
$thumb = wp_get_attachment_image_src( get_post_thumbnail_id( get_the_ID() ), 'full' );

if ( $thumb && is_single() ) {
    ?>
 <div class="bg-featured-image"></div>
    <style type="text/css">
       .bg-featured-image {       
            background-image: url('<?php echo $thumb['0'];?> ');
            background-attachment: fixed;
            background-size: cover;
            height: 100%;
            position: fixed;
            width: 100%;
            z-index: -99;
            -webkit-filter: blur(10px) brightness(110%);
            filter: blur(10px) brightness(110%);
            -ms-transform: scale(-1.1,1.1);
            -webkit-transform: scale(-1.1,1.1);
            transform: scale(-1.1,1.1);   
            margin: 0px;
        }
    </style>
    <?php
}
?>

Awesome, thanks for posting the solution :)