As a first thought, yeah you could try to get close with that but the object is still getting information from light sources, so they will reflect light anyway. In this case, for a dome, that isnt practical, and depending on the setup you did on the scene, the dome can reflect the lamp at a point that it ends up looking like you have two suns, on opposite directions. (I just suffered from this haha)
My solution at first was like you said, I turned off specular, env reflection but still I had the reflection from the lamp. So the only solution I had atm was changing the map, and turning on emission to avoid a major interaction with other light sources.
I read about you are working on a better material editor, thats really nice. Anyway I just posted this because if it has an easy and fast solution to be implemented, it would be really cool to have it.
Thanks for answering this fast!