Keeping a Shapes Area

I was wondering if there was a way to have a shape at a certain area and keep that area if I make that shape into something else.

For example:

I create a rectangle with area 4 in^2. I want to take one side of that rectangle and move it. What I want to do now may be magic but when I move that one side of the rectangle I want the opposite side of the rectangle to move accordingly to keep the area of 4in^2.

This is a basic idea of what I want to do but ideally I would like to make a rectangle into an oblong shape with the same area. Any ideas?

Look here, but it's a routine written in lisp, won't work in LT.

http://www.theswamp.org/index.php?topic=2117.15