No you can't get the fixed cameras without a data connection in Tomtom Go Mobile app.
Turn on 3G/4G (or wifi), then start Tomtom Go and plan a route.
The app is going to download fixed cameras, but only those "along your planned route".
Then you can turn off you data connection and start your trip.
Fixed cameras are downloaded only when you plan a route and only the necessary fixed cameras for this route.