@minihack - Haha, I was thinking about this exact same idea for when I eventually get around to starting my G5 mod! Had been keeping it secret because I hadn't seen anyone do this yet but sounds like you'll beat me to it!
With regards to the lack of an 'eject button' on the G5 I was thinking about something like an IR sensor fixed behind one of the little mesh holes above the drive bay (facing up towards the 'handle' on the top of the G5 to avoid accidental triggering of the circuit). Wave your hand in the space above the drive (underneath the handle) and the drive would eject for you. At least that's the theory!
I've also been looking for a touch sensitive switch (resistance based) that could be mounted inside the case near the optical bay and which would be triggered just by touching the case around the drive bay. Not sure how feasible this last one is though... by the time the case is painted, it might effect the conductivity too much and the switch/sensor wouldn't work.
Anyway, I'm very interested to hear how you get on with hacking that DVD drive.
EDIT - good point about powering the drive and thus its lack of suitability as a system drive - hadn't thought of that!