I've done it, but with a modified intake manifold. The stock unit sits to far down in the valley, I cut bottom out of mine and raised the floor. This created enough space to mount the coils. I've also done it with an MMR intake mani as well.
It was actually less hassle just moving the coil packs and they have proven to be more durable/reliable then COPs as well (at least in my applications.)
Never experienced any issues with them due to heat so I can't comment on that. I know with the MMR intake there was plenty of room for air circulation.