Hi James,
I think we don't have build in, but I think we should have a workaround for implement it if add information after request can make it works.
If you are using GoogleMapsLayer, you can modify the sendingrequest like this: googleMapsLayer.SendingWebRequest += googleMapsLayer_SendingWebRequest; And you can add the information for each request.
If you are using GoogleMapsOverlay, you need to try implement that by JavaScript code.
Regards,
Don