You will need the following materials:
48" of 1/8" steel (square section preferable but rod could work)
1 16 penny nail
tape and/or thread and/or super glue
And the following tools:
Step 1: Bend & Cut
Put a uniform 10 degree bend 3 inches from one end of each piece
Cut the point of a 16 penny nail off such that the head and shank are 3 inches long
Step 2: Bind and Tie
Bind each piece to the nail with thread or tape. If you're using thread a figure-8 twist will hold the pieces tight to nail while allowing other pieces to get tight too. This is tricky, you want everything bound up tightly, proceed with caginess :)
If you're using thread then repeatedly and tightly wind the thread around the assembly. Use super glue to cement threads together. Wrap the assembly in tape. This will serve as your handle. Leave the top exposed, you will strike the exposed steel ends with a hammer to drive the headset cup out.
Step 3: Usage
Insert the handle end through the cup and up through the head tube. The splines will snap into place (on top of the bottom cup) as you draw the tool up.
Loosely hold the handle while striking the exposed ends of the steel pieces. Ensure that you are driving the headset cup out squarely, you do not want to risk damaging (ovalizing) the head tube by driving the cup out haphazardly.
As the cup exits the frame be prepared to catch it so that it doesn't fall and get dinged.