I haven't ever had a problem with getting enough Rage on Malakk to keep SD up during Frozen Blows. Something to remember is that outside of Frozen Blows you should only use the first charge of SD, and spend excess Rage on T&C then FR. When Frozen Blows is up, then you start popping SD on cooldown until it's over, and repeat.
You could try saving Rage cooldowns (Incarnation, Berserk) for Frozen Blows, and see if that helps.