This is best taught when your ferret is young. I use my bed since it is the perfect height for my ferret to reach my arms or shirt that I've made into a hammock. Wear a shirt that has plenty of room in the front.
Bring the bottom of the shirt out toward the ferret so that it forms a ledge or temporary hammock.
Let your ferret see the treat, then put it in your shirt. Start close to the bed so your ferret will walk off the bed onto your shirt.
Once your ferret realizes that he's not going to fall and there's a treat over there for him, he'll go without hesitation. Now take a step back from the bed, he'll have to take a small leap to reach his treat.
When he's comfortable doing that, take another small step back. He should soon be taking a good leap to reach your shirt. Just remember, ferrets can't fly, so don't step back too far.
Once your ferret trusts you not to drop him when he jumps to you, you can try holding the treat in your hand and calling for him to jump. Not all of mine will do this, and the ones that do, I have to watch very carefully.
Bambi, at any given time will take a flying leap towards me expecting me to catch her every time. Unfortunately, she doesn't always do this while I'm facing her. There have been times when I'm walking away with my back towards her when I hear a thump.
She's almost given me heart failure a couple of times when she's managed to leap from the bed onto my back. There I was, dropping everything I had in my hands to reach behind and grab her before she landed on the floor.