First you want to go around the edge with a paper piercer. Pierce holes in even increments. It takes a little bit of time, but is well worth it in the end when you have a pen stitch that looks real!
Next, use a pen to draw lines in between your pierced holes. Be sure to "follow" your stitch into the hole so the ink gathers a little bit there, creating your authentic-looking "stitch". Don't worry about them all looking the same. It will look more realistic if they vary a bit.
When you are finished you have a stitched border that looks like you spent hours creating it!
Here is another example of pen-stitching. You can create intricate-looking swirls and other designs! Let your imagination go wild with this technique! Have fun!