The product installs in the VPC images of WCF 4 and Dublin should be expiring around now if you've been using them. Since an updated preview isn't available, here's how to keep them going.
Since disabling clock synchronization causes the virtual PC's time to only advance when it is running, a fresh installation should last as long as you need. You can repeat this process as many times as necessary though.
Jeff Beehler has a more detailed explanation.