Use redirect after content creating and use $node
Use arg(1); - (nid of the current node) in the hook_block_view and pass it in the link

function mymodule_block_view($delta = '') {
  switch ($delta) {
    case 'your_block':
      $nid = arg(1);
      $block['subject'] = 'Share by mail';
      $block['content'] = '&lt;a href=""&gt;share?nid='.$nid.'&lt;/a&gt;';
      break;
  }
  return $block;
}


Once you do that, you can make your thank_you page react on the nid argument by loading the node: 

$node = node_load($nid);


and extracting from it whatever you need