I can't test it right now, but can you try this?
In Scene_Battle 4, around line 130 should be this
if @active_battler.hp > 0 and @active_battler.slip_damage?
@active_battler.slip_damage_effect
@active_battler.damage_pop = true
end
Add this extra bit to the if-statement:
if @active_battler.hp > 0 and @active_battler.slip_damage? && !@active_battler.current_action.forcing
Theoretically, this should prevent slip damage from happening if the action was forced, which it is if done through an event command.