Update: I did it like this now: http://www.pushon.co.uk/blog/wordpress-contact-form-7-intelligent-thank-you-pages/
and put this in the custom page template for my forms:
<?php if($_SESSION['formdata']) { ?>
<script type="text/javascript">// <![CDATA[
jQuery('#order-firstname').val('<?php echo $_SESSION['formdata']['order-firstname'];?>');
[...]
<?php } ?>
The problem now is that after submit, the form is empty and only shows the stored session data after page reload. I want the data to appear directly after submit.
Any ideas how I can solve this?
Thx
joschi81