Error on sidebar's checkout button URL with IWD OPC extension [closed]

Question

I have installed the IWD One Page Checkout extension on Magento 1.7.0.2, default theme.
The url in the sidebar checkout button URL isn't correct: it send to the default magento checkout ("../checkout/onepage").
Instead, the "top link" checkout link and the "checkout" button in the "cart" page works fine (sends to "../onepage"): the layout file "iwd_opc.xml" overwrite the checkout cart link.
Maybe I need something like this also for the sidebar's checkout button?

ps: changing template/sidebar.phtml from

<button type="button" title="<?php echo $this->__('Checkout') ?>"    class="button" onclick="setLocation('<?php echo $this->getCheckoutUrl() ?>')"<span><span><?php echo $this->__('Checkout') ?></span></span></button>

to

<button type="button" title="<?php echo $this->__('Checkout') ?>" class="button" onclick="setLocation('<?php echo $this->__('../onepage') ?>')"><span><span><?php echo $this->__('Checkout') ?></span></span></button>

It resolve the problem, but it's not an elegant solution...

thanks (I accept every suggestion..)