Steering wheel holder required?

I've done some googling but it isn't exactly clear if a steering wheel holder is required if your wheel locks when removing the key from the ignition. I have a 2008 Mazdaspeed3 which will lock if you turn the wheel a bit when parked. Is that enough to hold the steering rack when doing toe adjustments?

Avoiding buying a tool I don't need if necessary :)

In my experience, different steering racks might be different, the resistance in the rack itself is enough to keep it from moving even without a turnplate. Small adjustments will just twist the tire slightly, large ones might shift it and the steering wheel with it. Make sure to rock the car back and forth before you measure for the final setting, as that twist can alter it slightly.

However, I just went and bought a handful of cheap plastic cutting boards, sandwiched some grease between two, and put them under the wheels as turnplates. The built in lock is enough to hold it, but it's not always centered.

On our race cars, we just center the rack, and drill a small hole straight down that goes through the housing and into the rack (not far, perhaps 6mm (1/4")). When doing an alignment we just drop a drill, bolt or rivet (depending on hole diameter) into the hole. Rack stays centered as you adjust the toe.

As the vehicle should be prep'ed as it's going to be used, if you use the driver, or someone of similar weight, in the seat you can have them hold the wheel still?