Pin him. Surround him with summoned creatures, so he can't run away. Raze is not smart enough to jump, so if he turns around, you can just use active pause and disable the regenerator before he reaches it. It's easy. If you're melee, you can also pin him to a wall, he can't run away then either.
Just remember: if he does turn around and heads for a regenerator, activate pause immediately, then jump over the summons and pull the lever before he enters the regenerator. You're faster than him, so it shouldn't be a problem.
