This is another way to hop! Instead of hopping while you're on the pedals, hop while standing on the tire, with one foot on either side of the frame.
For learning how to do it, we stepped up to the tire from the ground and practiced just hopping until we could do it consistently. Now we are practicing jumping from the pedals (while hopping seat-in-front) up to the tire. Eventually we will learn to transition back to the pedals.
For learning, there are two ways to get up:
1. Step up one foot at a time. Place the first foot on the tire, right against the frame. Tilt the uni a little bit toward the side with the foot on the ground, so that when you step on the tire it won't roll away. Then step up with your other foot, placing it right up against the frame on the other side. Try not to put much weight on the first foot while you're getting up.
2. Jump up with both feet simultaneously. Hold the uni straight up and down in front of you, then jump and nail the tire on each side of the frame, leaving no spaces. When you do this, look OVER the top of the uni and watch your toes.
Now you're ready to hop! Keep your legs locked, grab the seat on each end with both hands, and jump with the balls of your feet. Try to get as many hops as possible. Look out in front of you. When you feel yourself losing balance, try to hop in such a way to correct the balance. It's fun and it looks pretty cool!
To be able to truly do this trick, you have to start and end it on the pedals. To get into hop-on-tire, learn to hop seat-in-front until you are comfortable with it. Then you have to jump OFF the pedals, twist the uni a quarter turn, and land on the tire, with your feet close together, and keep hopping. It works - don't give up!
As far as returning to the pedals, I think this is the trick I find most frustrating... However, I learned it. The method I use is to make your hopping stable, stop and crouch down so there is a space between your legs and you can twist as you push the seat between your knees, then sit on the seat with all your weight on it. Only then do you start wheel walking out of it. Don't rush. Some people have more success with simply jumping right back down to the pedals.