My method is a booleaned sphere (has to be booleaned.) with a HDRI map on it, then take lights and group them up against the inside of the sphere where the 'light' would come from, IE if there's a window, I arrange the lights by the window, as well as any other light sources. Then either just stop there, or apply a semi- sphere of non shadow casting lights set to extremely low values and varying colors depending on the HDRI. I have found that this is the best way (that I've experienced atleast) to simulate GI.