Global attack modifier for NPCs?

On my "D&D 5E by Roll20" character sheets I have the "global attack modifier" field activated. Very useful for bonuses like the Bless spell. Now my group will face some enemies who also have access to the Bless spell. But I can't find a "global attack modifier" field on the NPC character sheets. Is there an easy way to give an NPC a temporary bonus to attack without having to edit all his actions?

I've looked through the attributes and couldn't find anything. I just do it mentally at the table. You could put [[1d4]] on a macro or token action button to make it quick and easy to roll on demand.