If you don't use focus for your assisting on your second mage, you could use a focus sheeping macro.

#showtooltip
/clearfocus [modifier:alt]
/focus [target=focus,noexists]; [target=focus,dead]
/clearfocus [target=focus,help]
/cast [target=focus,harm] sheep

With this, you'd be able to keep 2 mobs cc'd, but you'd have to keep that macro/keybinding on roundrobin in keyclone.