[kh99]

You should be able to do this (use ob_get_clean() instead of ob_get_contents()):

ob_start();
  require_once('LOCATION OF EXTERNAL FILE');
  $php_include = ob_get_clean();

  require_once('LOCATION OF EXTERNAL OF SECOND FILE');
  $php_include_SECOND_FILE = ob_get_clean();

ob_end_clean();
vB_Template::preRegister('TEMPLATE YOU ARE USING',array('php_include' => $php_include));
vB_Template::preRegister('TEMPLATE YOU ARE USING FOR SECOND FILE',array('php_include' => $$php_include_SECOND_FILE));

I think if you want you could also put a preRegister call after each call to ob_get_clean() so you wouldn't need a bunch of different variables.