Fearing the Shackle or Banish target is also useful in a pinch if the Banish pops early, get the pally to fear it then re-banish.
Just get the pally to create a Macro to set the Banish as his Focus and set up the macro to cast Fear on your Focus target that way the pally can cast heals on the tanks without dropping his target to cast Turn Evil.
For Example...
#showtooltip
/clearfocus [target=focus,dead][target=focus,noexists]
/focus [target=focus,noexists]
/script SetRaidTarget("focus", 1)
/cast [target=focus]Turn Evil
/stopmacro [nogroup]
Checks to see if your Focus is dead, if it is it clears the focus, if not it attempts to Assign a Star as the mark and Cast Turn Evil. It does it without dropping your current target.