Yes there is, I mention this in the article actually.
What you need to do is go into photoshop and split your image into two -- the RGB color channel (basically combine it with a flat white or flat black background and flatten it), and the Alpha channel (reveal the alpha channel, save that out as a monochrome black & white image).
Then you XBR each of those images separately.
Then, you go back into photoshop, and recompose the image, taking the new upscaled RGB image, and setting its alpha channel to use the new upscaled Alpha channel. Then save that.
That's a tedious process of course, which is why I automated it in my home grown tools. How many images do you have to process?