How to put a variable on postbits?

[ThorstenA]

I wrote a showthread plugin and want to address the place between first and second post with this template hook:

$template_hook[postbit_end]

This works fine:

  eval('$template_hook[\'postbit_end\'] .= "Test abc";');

However these do not work:

  eval('$template_hook[\'postbit_end\'] .= "' . fetch_template('persforums') . '";');

eval('$template_hook[\'postbit_end\'] .= "$persforums_variable";');

Do I have to make the $persforums_variable global? How could I do that? Or is there an easier way to just put the output on ad_template[showthread_first_post]? How could I adress this place?