Imagery Service Visibility

I have a number of image services in my Geocortex site and the user has the ability to switch on their visibility at runtime.  These are ArcGIS image services.

How do I determine in a workflow whether the user currently has a particular image service switched on or not?

The image service doesn't have any actual 'layers' as such if you look at its REST endpoint in a browser.

I've tried using the GetLayerVisibility activity with the 'map service ID of the image service.  This activity doesn't work without either a layer ID or layer name though.  Hence I've tried various layer IDs and layer names but none of them are valid, eg. "0", "1" for the layer ID don't work.  Using the image service name for the layer name doesn't work.  Using "%" or "*" don't work either for either of these.

I've also tried a DownloadString activity to query the REST endpoint of the Geocortex site but the 'visible' value of the image service is always 'false' regardless of what the user does at runtime.

"http://server/Geocortex/Essentials/REST/sites/sitename/map/mapservices/" + cstr(item) + "?f=json"

Can anyone help?

Mark Norbury