Or put him on passive (ctl+2 default). Just remember it's a toggle so you have to turn it off.
But really, if you're in stealth, companions will only attack if you're spotted and pull agro. Stealth skill decreases with level difference, so you really it's best to take a wider route around the packs if you're being spotted. Also keep in mind that frontal and side detection went way up in patch 1.4. Even trash mobs of the same level will see you if you stand in front of them.