Identifying a unit which casts reveal from goblin laboratory

[Zepher]

I was trying to figure this out in the past but wasn't able to,

Suppose you have a unit come to the goblin laboratory and cast reveal, how can you set up a trigger to store to identify this unit (store it as a variable, etc.) I can't seem to find a way to do this since using "casting unit" refers to the neutral lab structure, any suggestions ?