Assuming everyone else is as defective as I am and took forever to figure out such a simple thing, this is useful information.

Use a two stage buff application with the first being a placeholder file just to make the target ship be LastSpawner, and have it call the second buff with an OnDelay interrupt and a LastSpawnerNoLongerHasBuff finish condition referencing the buff you're after.

You can do other things with the method too, like having a ship that only buffs other ships of the same type, but it is all kinds of messy and should be used sparingly for purposes of cycle munching.