Step 3: How To
The trick to this is you hide four cards behind the jacks as you are showing them. Then when you put them back on the stack there are four other cards on top.
Once you lay the eight cards on the top of the pile, take each of the top four cards and put them somewhere differently in the pile, all the while being careful that they think the cards are jacks(you can tell a story on how four jacks are on the roof of a hotel. The police come and they have to scatter to different floors)
After the top four are scattered, reveal the four jacks on top.