Thanks Erel, this seems to be the official method but whether the icon in the notification tray is shown or not is up to the OS and how many notifications are visible. In my case the icon still shows.
Doing some further research it seems that the only way to guarantee the icon is not shown is to use a black icon and push it to the right (max priority?).
I think for now I will just stick with letting the user choose if they want the notification or not.