My Bread Maker Instructions tells me to proof my rolled out pizza dough for 20 minutes, at 40 degrees celsius (105 degrees fahrenheit). How do you he

I wouldn't worry about either of those numbers to any great extent- a lot of people don't proof it at all at that stage, but I do think it's a good idea. The oven with a pilot light is an old solution, or dsullyo's water trick aren't too practical since presumably you're preheating the oven; I sometimes place pizzas in the heat from my oven vent on cold days (you have to be careful not to get it hot enough to kill the yeast) microwave is big enough. I also sometimes use hot water in the microwave to warm things; they're usually well insulated, but probably not big enough for a pizza. Proofing for 20-30 minutes at room temperature should do well enough- it's really not a very precise operation.

Hey Chris, Cooks Illustrated has this hack.
Put your dough on the middle rack of your oven. Put 3 cups of boiling water into a container and put on the bottom of your oven. Close the oven door. This should hold enough heat to proof your dough.