Actually pretty banner procedure help

So I’m trying to make a custom model for new banners in my mod, one that actually looks good. I have this planned out as the theory of what I’d have to follow in order to get it to work 

The idea is I would make 3 custom models, each one is one block tall, the top, center and end of the banner. I need to make a procedure that when you place the item banner, it places the end piece below it, the end piece would have no hit box. Then if you click again under the first piece, you add a middle piece, replacing the previous end piece and spawning a new one under that, so you could keep on going on and on and make a really long, really pretty banner. The issue is I have no clue how to even start a procedure like this, would anyone have any idea how I could carry this out?