Custom Image Sizes: Force aspect ratio?

I am trying to make a custom image size.

What I need is for the image to have a width of 120px and a height of 90px, regardless of the image aspect ratio.

From what I can tell, setting crop to “true” will always respect the original aspect ratio.

So, for example, with an (original) image that is taller than it is wide (“portrait” orientation), the custom image size will also be in portrait orientation, even if the size is still smaller.