Actually what he's trying to do is pretty common in most image editing programs. I'm also looking for that function. It's quite handy for adjusting images for distance variations such as your signature image...
These are done with a simple selection editor in a program called Serif PhotoPlus called a Deform Tool, it has a center that can be moved, and all the 6 nodes can be pulled around the center, shifted, alted, ctrl'd and combo's of them to get a desired effect. A few of the deform tools effects are equal to just adjusting the size of the selection, but it's the corner pulling effects that we need, and in a tool(button), not plugin.
Original
Deformed - bottom left corner stretched
Deformed - bottom left corner stretched and mirrored diagonally
Deformed - bottom left corner stretched and mirrored horizontally
It also does vertical mirroring. The effect is actually quite nice and needed, check it out (for research of course) it's free.