At the present time there isn’t any way to send commands through Alexa in that fashion. That’s something that Amazon would have to open up, and they haven’t.
What some people have done when they had a device they really wanted to integrate with SmartThings, but the only available integration was with echo, was to get an inexpensive android device, literally set it next to the echo, and have it speak the appropriate commands using LANnouncer or similar method.
Obviously, that’s a hack, and is it fairly complex set up, but it will work and there are some people using it. 