You can just type them, but if you're going through the bottom object thingy in your event window, they're called "Get X position of * edge"... I'm thinking that if you nest some loops into movement to test overlap of objects, then individually test the edge positions, it could work? Will try it, but really don't know if it's any more efficient to introduce new queries.
Edit: Okay, I figured out a way to do it without either system. Dunno if it's accurate, but the result looks fine to me.