Sizes for those holes vary between mods so it is hard to say what could be good for you.
What I did with the foil was that I first glued the foil to a piece of regular paper. Then I cut it to a right shape, bended the edges a bit and glue it behind the hole. On top of that foil I usually place the lego char with glue. As you can see from the following image, the led is positioned so far back that the foil will settle before it and not over it.

_________________
Metku |
AlltheMods |
LedCalc |
Teknolelu |
AndroidCodingMain Computer: Intel i5, MSI H55M-ED55, 12 Gigabytes of DDR3, 3 Terabytes of HDD, GTX295 and Benq 27"