functions.php

<?php

/**
 * Add CTA Banner
 *
 */
function be_cta_banner() {

  // Only run on archive pages 
  if( ! ( is_home() || is_archive() ) )
      return;
  
  // Only insert before first and fifth posts.
  // Note: Post count starts at 0
  global $wp_query;
  if( in_array( $wp_query->current_post, array( 0, 4 ) ) {
      echo '<div class="cta-banner"></div>';
  }
}
add_action( 'genesis_before_entry', 'be_cta_banner' );