What about the on-board leds? power, activity, network. Is there a control for these?
Take a look at the RasPi schematics. The power LED is hard-wired to 3.3V, so the only way to turn it off is to remove it or its current-limiting resistor. Activity is controlled by the BCM2835 SoC, probably in the SD card driver. You might be able to override it by changing the GPIO that drives the Activity LED from an output to an input. The network LEDs are controlled by the LAN9512. You can in principle control them by modifying the LAN9512 driver -- have fun with that. It may be that someone has already done it and posted the results.
