I’ve looked for this some time ago.
Best thing you can do is change the default contact form.
Filter you can use: wpcf7_default_template
Info can be found in contact-form-7/includes/functions.php file line 63
The filtered variable is:
$template="<p>" . __( 'Your Name', 'contact-form-7' ) . ' ' . __( '(required)', 'contact-form-7' ) . '<br />' . "\n"
. ' [text* your-name] </p>' . "\n\n"
. '<p>' . __( 'Your Email', 'contact-form-7' ) . ' ' . __( '(required)', 'contact-form-7' ) . '<br />' . "\n"
. ' [email* your-email] </p>' . "\n\n"
. '<p>' . __( 'Subject', 'contact-form-7' ) . '<br />' . "\n"
. ' [text your-subject] </p>' . "\n\n"
. '<p>' . __( 'Your Message', 'contact-form-7' ) . '<br />' . "\n"
. ' [textarea your-message] </p>' . "\n\n"
. '<p>[submit "' . __( 'Send', 'contact-form-7' ) . '"]</p>';
Hope this helps.