I'm not sure if it's been said yet or not, but I know of a really easy way to get backfire pics in photodrive. First pick your location, and car. Now when the drive starts go to the spot where you want the backfire pick to be taken. Then, using the right analog stick, bend it downwards so that the brakes come on. Now you will want to hold the accelerator down at the same time, so use the X button. If you have the brakes just right, which is about 2/8ths braking pressure, or just near the bottom the accelerator should dip down even though you are holding the X button all the way down. Now your car should start reving and backfiring while you are just sitting there.
The one drawback is in the picture your wheels will not be moving. I only tried this with my '02 GT and it has dark wheels, so the picture still looks like it's moving. Hope this helps some people, and if you have questions please ask.