Cut the top
Draw a large circle on the top of your pumpkin. If you're feeling smart, throw a nice notch in there. Cut out the hole using your pumpkin carving tools or knife of choice.
Map the holes
Using a pencil, pick a location as the center spot. Chart holes that are approximately 1.5" apart. Since the surface is spherical, the holes on the top and bottom row will be closer together than 1.5" apart.
Drill pilot holes with a 1/4" bit and then larger holes with the 7/16" bit. Test the holes with a pixel and go with a larger bit if needed. A 1/2" bit may work better, so it's good to have both on hand.
Position the button
Fold two diagonal button legs back or remove them. Pick a place where you'd like your button to sit on the outside of the pumpkin. Given the length of your wires, you probably won't be able to have it sit too high on the pumpkin. Push the legs of the button into the pumpkin to create a couple small markings.
Drill button holes
Drill the two button holes using a 1/8" bit. Feed the male jumper cables attached to the button into the holes to that the button sits against the pumpkin.
Clean your pumpkin and insert your pixels into the holes. The first pixel that receives data should be in the top left hand corner. Your pixels should be laid out in a zig-zag, back-and-forth, or serpentine way, so that the 9th pixel is directly below the 8th.