i want to connect a second remote to the little dongle in the back of my TV

That would be the Gemini Air for DIRECTV STREAM.

Originally you could only pair a single Gemini remote to it. There has been mention this may have changed, so hopefully another poster (perhaps a fellow ACE) can clarify on this.

You can have 2 remotes programmed for the Gemini Air.  All you have to do is go into the settings. Then go to System, then go down to Remote & Devices, then add Directv Remote and follow the directions on the screen.  Then you will be all set.  I hope this helps!