I hear you that would be wonderful, but I could compromise with workarounds because I want it bad. If I'm not mistaken it's just outgoing calls that are effected by the second number, could definitely be mistaken
Outgoing calls or texts will only show the watches number if the your main phone is off or not connected remotely. Otherwise, it's transparent to the person on the other end. Just the same if you're not connected remotely or your phone is off if they call that number they will go to voice mail.
You don't necessarily want to give out the number of your Gear S as 99% of the time it WILL be connected either via Bluetooth or remotely in which case calling it directly will result in the call going to its voice mail.