I fed my enormous adult H. longimanus full-grown Blaberus fusca roaches without a problem. As long as the roach isn't so big that your scorp couldn't handle it with his pedipalps, it should be fine.
Just remember, if your scorp refuses prey for more than a day or two, just take the prey out and try again in a week.
And he won't get larger, sorry.
If your emperor scorpion stops eating, don't panic.
Be nice -- you were a noob once, too
"Never ask an engineer to explain something, because he will."