Solved this problem using the following code:
<?php
add_action('genesis_after_post_title', 'cause_header');
function cause_header( $field_options ) {
global $post;
$cause_image = get_post_meta( $post->ID, '_pfund_cause_image', true );
echo '<img class="pfund-image cause-header" width="625" src="'.wp_get_attachment_url( $cause_image ).'">';
}
?>
A few disclaimers: I'm using the Genesis Framework from StudioPress, so the add_action is using a Genesis hook... regardless, you should be able to use the code.
Class and Width are arbitrary; modify those as needed.
This code could probably be improved with an "if" statement, but this is doing the trick for me. Hope it helps someone else who is trying to access the pfund image from external PHP.