I love this one! If you ever perform the signed bill in Kiwi, try it. The point is that you have an unprepared Kiwi on the table. In your pocket, there is a prepared one (with the hole in it). In the course of the routine, you vanish the borrowed bill and secretly load it (under some pretext) into the Kiwi in your pocket. The video shows how you will switch the Kiwi on the table for the loaded one.
It is hard to explain, but the whole switch happens in a sort of 1–2‑3 rhythm. I am sure you will get the handling of it …