From the Google Checkout blog…
Starting today, merchants will be able to use existing affiliate tracking and analytics tools for sales through Google Checkout. You can now include a pixel URL with parameters in the cart post and it will be included on the Checkout Thank You page. You’ll also be able to include placeholders for dynamic variables that will be populated before calling the URL. For more details, refer to third-party conversion tracking in the Google Checkout API documentation.
And here are more technical details on Google’s support for third party conversion tracking.
Quick fix or long term solution?