When I found cupcake liners that claimed to be able to hold up to baking without a pan, I was skeptical. But that didn't stop me. I gave them a try.
They come in several sizes, colors, and configurations. Here's the package for one of the sizes:
Amazingly, these hold up pretty darned well. Of course you can mangle and flatten them, but if you fill them without mashing them, they keep their shape, even when the batter misbehaves. Here's a case in point. The cupcake batter over-rose and didn't set (a common problem here at high altitude) and it dribbled over the side of the cup. The cupcake isn't pretty, but the paper held up well.
Another benefit of these extra-sturdy papers is that they peel off well. I've had cupcakes and muffins where the papers have torn when trying to remove them. No such problem here.
The papers are more expensive than standard cupcake papers, but they're not the standard flimsy papers. It's an interesting product.