The same way I deal with mobs of Ork Boyz moving through cover.
Sheer volume of fire.
And if you're going with a Dred Mob or a Battlewagon line, is easier, because you can focus more of your fire onto fewer targets. Just focus on bringing one down at a time, rather then spamming fire across the line.
Oh, and there's always the "run in and punch them in the face" option, too, since the KFF does SQUAT at close quarters.
Only recommended to capable assault troops, obviously.
"I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain."
-The Bene Gesserit Litany Against Fear, Dune
The Swordsworn Chapter WAAAAAAGH! GOBSMASH
W: 1 T: 1 L: 6_________________W: 8 T:2 L:6