Anyone know of a "backyard" method to put the temper back in an EZ-Out?

As someone that used to forge custom knives, getting the temper correct using a quench fluid is going to be difficult without a lot of trial and error.

Do you have a Rockwell hardness tester on hand?

It'll be far cheaper to just replace it. If you anneal it too much - it'll bend like gumby. If you harden it too much - it'll shatter.