Global Lighting for Android ES3.1 (HDR Disabled)

I’d like to add a minimum amount of ambient light to the world. The game is set in the sky so there are no fixed reflective surfaces for indirect lighting. I have a sky sphere with a movable directional light for the sun. It lights up surfaces facing the light, but other surfaces have zero light and appear black. The only solution I’ve found is to set the emissive colour in each mesh material. Are there any other options?

If anyone else ends up here, I found adding a skylight with a “Lower Hemisphere Color” achieves the desired result.