This seems to only be available to devices capable of a mobile data connection. My WiFi-only Nexus 7 doesn't have the options while my Galaxy Nexus does. I suppose the utility of this service would be limited on a true WiFi connection, but I commonly use my GNex's hotspot capabilities. It's a shame that it seems I can't use this over that connection.

Edit: Seems there's a newer version, but the Play Store tells me it's incompatible with my Nexus 7. That would explain the missing flag.