Can someone remind me how I was able to do this (stretch the image) in either Photoshop or Illustrator? It's been awhile and seems like I forgot how I did this trick.
If you mean the way columns of pixels are "stacked up", you could do this (although it seems rather awkward):
Add enough Canvass to accommodate the stretch. Select half your image, and Option+T to Transform a Copy. Put a value of one or two pixels (relative) in the Y field of the Options with everything else default. Commit the Transform, and without deselecting, Edit > Transform > Again a LOT of times.
An easier, but more limited, method is to use the Single Row Marquee tool, and New Layer Via Cut. Edit > Transform the new layer with some pixel value in the H field, not a percentage. Put this layer below the original. Select half your original layer, and drag it away from the other half to reveal the lower (stretched) layer:
The first method I gave can follow a smooth curve nicely, but it's very tedious. The second method only works with a horizontal row, but you could still seperate the two halves by cutting along some other line, if the subject allows it.