Paint.NET :: Game Textures - Creating Alpha Fade?

I make game textures. What I want to know is if there is a plugin that can create an alpha fade? So that, lets say, on the left side remains no alpha, but heading toward the right is a gradual fade into alpha.

The regular transparency plugin allows either the entire image or a selection within the image to become alpha. A way to simulate this is to make an image half black and half white.

Next select gaussian blur to have both sides bleed into each other from white to black then click black to alpha plugin in and that creates a fade from white to alpha. An alpha fade from the white to the black side of the image.

But I was hoping that there is a plugin that could ignore colors and create a gradual shift into alpha from one side of the selection to the other.