The tough part is reaching in and grabbing him. Practice to make the chase as short as possible. Even the young igs are tough so don't worry about grabbing him. He will slowly get used to it and eventually lose his initial panic reaction, even though he may continue to try to evade you.
Right now neutral territory starts just outside his cage. In the future he will claim new territories, so you will have to be alert in finding easy territories where he can relax. In all the years I've had igs, none ever claimed the sofa so that was always a safe, comfortable place to do the initial taming.