Ok so here is a method to spawn helpers for sprite objects. It will work even if every single tile is the same, but will reduce the loops required if your corners are already defined. Basically you check if your block is a corner, and then you check the space to the left or right of each one to see which side is open. Then based on that you will spawn your helper block at the correct position.
Set up: For your corner animation frame in your block object, make two image points, one in the top left and one in the top right.
For each BlockObject
Compare Values AnimationFrame is CornerFrame
BlockObject is NOT overlapping at offset BlockObject.Y+BlockObject.Height (Check to see nothing is above it)
BlockObject is NOT overlapping at offset BlockObject.X+BlockObject.Width (Check nothing is to the right)
Action: Spawn HelperBlock at BlockObject's imagepoint top right
BlockObject is NOT overlapping at offset BlockObject.X-BlockObject.Width (Check nothing is to the left)
Action: Spawn HelperBlock at BlockObject's imagepoint top left
Note that for this method if there is a single block by itself, it should spawn helpers on both sides. Up to you if you want that to happen or not. If you don't, you can add an ELSE to the second subevent.