According to this document from Citrix:
Integrated Voice over IP connections are configured to work outbound through UDP port 8200. Integrated webcam video support is configured through UDP port 1853
So you can use these two ports to identify the GotoMeeting traffic by putting them in the "DST Port" field in the traffic identification interface. For example:
If those ports are not open on your network, then you'll need to use the IP blocks listed in the linked document, but this will need to be updated/maintained over time.