How to properly boil egg white?
You could microwave it, put the whites in a glass container with a loose lid and blast it, the texture will be very similar to a boiled egg. You might have to check from time to time for doneness.

It will harden in the shape of the container if you don't "scramble" it every 30s, and it might also explode from the steam trying to escape (hence the cover). Brush some oil in the container to make sure the whites don't stick.

Personally for that much egg I'd just cook them in a pan like an omelet, it's much less trouble.