Zion entrance hours - can you still drive in if you show up before the shuttles start?

Shooting for Moonlight in a day, which will obviously require a very early start. Not totally confident that we'll make it for the last shuttle though. When I was in Zion a few years back, we were able to drive in on the road because we showed up in the very early morning before the shuttles began. Can anyone confirm whether this is still the case? The NPS website says you can't drive on the road during the time of year that the shuttle is running, but AFAIK, they don't barricade the road or anything and you can just drive back there with no problems before the park "opens"

To further elaborate on Rob T's excellent info:

To drive in you need a scenic drive permit. You get this the day before at the wilderness desk at the visitor center. This allows you to drive in and park before the shuttle is running, and allows you to have a car there after the shuttle runs. You'll need your car make, model, and license plate number. Tell them you will be starting before the shuttle is running. These permits are only for long days, not overnights.

Also, if you're planning on doing it this week, check the weather. It already rained today, and will probably keep raining all week. Please, please, please don't climb on the rock when its wet. Give it a couple of days to dry out, not just one. 

My partner and I drove to the Floor of the Valley Road fork, parked there, took the very first shuttle of the day, climbed Moonlight Buttress, and missed the last shuttle by 1 or 2 hours. The walk down the road in the moonlight was a great way to end the day, and I still look back on the walk with fondness.

We biked in this past spring. It's only 4 miles to the very back of the canyon, and a pretty easy ride. So to Big Bend it's roughly 3 miles. Plenty of sign posts, and trees to lock your bikes onto. You then have an amazing quiet entrance into the canyon, and a wonderful coast all the way out. Park right after the bridge across from the mouth of the canyon.

I've heard that there is an extra shuttle that runs after the "last" shuttle. If you miss that one, supposedly if you stop in the lodge after hours, they have some dude that will drive you back to the entrance.