There is a fake GI preset. Have a look at it. You do have to tweak the lights to get them right. You can do a lot with them tho. Distant lights are powerful.

Well the irradiance map appears to work if you do this. Gonna sound odd.

1. Set up your scene lights and make everything invisible.
   2.  Tell it to save a map in the irradiance map area choose static or multi-frame depending (scene or animation basically)
2. Then render with proper settings, but with nothing visible...takes no time.
3. Then go back and make everything visible
4. Then when you go to render choose the use irradiance map option and choose your map.

Should cut render time down 30+%, possibly much higher. If you group items they are easier to turn invisible.

No need to think outside the box....
    Just make it invisible.