First, place a mirror tower near the edge of the map that your cinematic will be at.

Then, create invisable walls around the mirror tower, and shrink it. Your "Sun" should be floating. If it isn't gloating, move towards the edge of the map or go to a low-pitch angle. this is what it should look like:

Then create a scene around your area. I'm not going to make a quite beautiful one, but in this picture I used the perspective method.

Use Render Sky. SkyBlue and SkyStormy look good especially, and the sun actually suprisingly well with Render Snow.

And walla! There you have a sun!