Take your 40 conductor IDE cable and count five of the little “wires” and place your thumbnail between conductors 5 and 6. Place your other thumbnail in the corresponding groove underneath the ribbon and using opposing pressure, “pull” the fifth and sixth conductors away from each other. After you get a good tear going it is easy to separate the conductors all the way from connector to connector. Do this slowly. Repeat this every five conductors until you have eight five conductor ribbons. Now carefully twist and stack the mini-ribbons on top of each other until you have a square bundle and using premium electrical tape wrap the bundle leaving an equal distant from each connector. Wrap every two inches until the point where the wires spread and make it impossible to continue. You will notice that the bundle wants to “lump” up because the middle ribbons are not being turned and twisted as much as the outside ones.
You can safely do this to floppy cables also, but I am unsure about ultra wide, and the new 80 wire IDE.
Of course the price of ready made IDE cables are low enough that anyone can afford them. And they will look a lot better too.