Here's my experience with two self-cleaning ovens:
Self-clean cycle will not engage until latch/lock is secure.
Once secure (door cannot be opened), the oven starts to heat.
Once the temperature of the oven reaches 500°F, a solenoid engages which locks the latch into place (i.e., you cannot unlatch the oven at this point).
The oven continues to heat to some very high temperature (unknown to me) which "cooks" off all the crud in the oven.
When the self-clean cycle is over, the oven stops heating and starts to cool down. Once the temperature reaches 500°F again, the solenoid disengages which allows you to unlatch the door.
Preheating the oven using the self-clean cycle is a moot point since you won't be able to get the door open until the temperature drops to 500°F again.
The only way to use the self-clean cycle to cook a pizza is to somehow circumvent the safety solenoid so that you can open the oven door whenever you like.