If it's always the same monster it gets used on, it should be easy to cast an empty skill, link it to a battle event, and manually apply it to the monster with Add State command.
If it's another random monster, apply a filler state to all monsters on the field. Have an empty self target skill that removes that filler state, link it to a common event that rolls 1-8 variable for each possible monster on the field, checks if the corresponding monster is applied with the filler state, and if they are, use Add State on them for the skill buff. Then re-apply the filler state again.