[pannenkoek]

Oh wait wrong code and not able to edit original post… here is the good one

jQuery("form.bbp-login-form").find(".bbp-submit-wrapper").append( '<button class="button" onclick="location.href=\'http://LINK-TO-REGISTER-PAGE\'" type="button">Registreer</button>' );

[pannenkoek]

And then I stumbled on to the same problem. I came up with the following solution.

Create a page and add the shortcode [bbp-register] to display the register screen.

Then add the following code to your functions.php

function add_bbp_register_button() {
?>
<script type="text/javascript">
     jQuery('.bbp-submit-wrapper').append( '<button onclick="location.href=\'http://LINK-TO-REGISTER-PAGE\'" type="button">Register</button>' );
</script>
<?php
}
add_action('wp_footer', 'add_bbp_register_button');
 

cheers