It is typical with any 12 string to use a slightly lighter gauge string than you would on a six string. The only problem I can see is that you are already using a .008 for the octave string in the G course, so you will not be able to find a smaller gauge string. You could make a custom set out of an extra light set and make up the octave strings out of singles. Check out D'Addario's website, and look at the gauges they have for the extra light acoustic twelve string set.
I had a Ric 366/12 that I strung up with .011s but the action was so low on that they felt like .009s... you can't get very big on the high G string, you understand.