Using a modified Aeropress plunger seal, I was able to get a rich, syrupy, esspresso-like flavor. Other Aeropress espresso recipes have similar strength to espresso, but seem to lack the complexity of a real shot. The donut seal is used to maintain the tamp when pouring water into the cylinder, and ensure complete separation of water and grounds until you begin pressing.
Keep in mind your Aeropress still needs a plunger seal on the end. So buy a new one and replace the old seal on your plunger, so you can modify the old seal.
This recipe uses a metal filter in the Aeropress cap and a paper seal above the grounds and below the donut seal.
Experiment with the grind, tamp, and water amount to get your desired strength and extraction. These parameters will also determine how much force you need to apply, and/or how long the extraction takes.
You will have to push quite a bit harder than a normal Aeropress recipe, so make sure your cup is sturdy (I use a stainless mug) and on a stable surface. Be careful when pressing so the cylinder and cup do not fly out.
To modify the plunger seal: Using an Exacto knife, or other sharp blade, cut a round opening in the center of the seal. Leave the flared outside edge intact. The opening in the center should be large enough to prevent channeling water through the center of the puck, without leaving the seal too thin/flexible to stay in place. Be careful not to cut yourself!
Give this recipe a try and leave a comment to let us know how you go!