google checkout in "onepage checkout" for magento

Hello, I own a website built using magento. I would like to use google checkout as my payment method. However at the moment google checkout can only be used when customers click google checkout image and they will straightly be directed to google page to make the payment. . i have installed one step checkout extension. So i would like someone who can make google checkout to be appear in "onepage checkout" page. Which means after they click add to cart, when they make the payment after choosing the shipping method on the onepage checkout page, they could choose to pay by google checkout. Thank you