If it has to be a skillshot,
Zilean Q, proposed changes
"Kobe" style skillshot >> Pass through line skillshot
Now marks all enemies hit with a bomb. After 3 seconds, the bombs explode, dealing magic damage to nearby units (each unit may only be damaged once by an individual cast, obviously). If an enemy with a bomb gets hit by another bomb, the first bomb is detonated early and everyone hit is stunned.
Maybe a linked fuse effect, so that if one bomb goes off early, they all do.