With Fawkes all you have to do is ask him and he will do it but I think Charon needs convincing with a speech challenge.
Without Broken Steel, you can't. You have to do it. Yeah, your companions would rather you die than they walk 10 feet and press a button. Just another way in which the FO3 story is an absurdist farce.
You could always do it yourself and be a hero and not a pussy.