The cloud nodes just volumetrically shade the incoming density function. So if you "stretch" your density function in some way (e.g. using a much higher value in one of the noise scale parameters vs. the others), then the cloud node will shade it that way. But it's the density function that's stretched, the cloud itself is just shading volumetrically as normal. In other words figure out how to get the shape you want ("stretched" look) in a normal shader network, then just feed that into a cloud node and it'll render as a volume. You can't "stretch" a cloud itself, so to speak.
- Oshyan