dont know if this will work, but maybe you could play around with it (im sure there is a way to just pass the paymentid to smarty from cart.php but that requires a little more thought)...
in order_message.tpl under the section loop, put
Code:
{if $orders[oi].order.payment_method nq 'Credit Card'}
display the non credit card order message
{else}
display the credit card order message
{/if}