This one is all about misdirection. No need for any double joints or knucklebusting skill, just the ability to focus your suckers' attention.

This ones easy: while you're setting up the but, position your body to draw focus toward the cork. Hunch over and get them to look closely too. This hyperfocus on the cork will allow you to slide the pen into your eat during the third drawback, effectively vanishing the pen for a few seconds.

Now for the important part. At the exact moment they realize the straw is in your ear, their guard will be down and all their attention on your face. At this moment, deposit the cork into your pocket. No need to be tricky about it, they're not event going to be watching you by this point.

Now you're set. With the cork ditched, keep your hand in a closed fist as though you're still holding the cork. Repeat the tapping motion, reveal your fist empty, and score your free drinks!