I agree with JAG. You can get a low pro nanner chopper, or adjust the base on a regular one to hit the 5" mark. Any shorter and you will lose feather height, which is a bit more critical on a banana cut.
Whichever you prefer, take two popsicle sticks and glue them together in a "T"....insert this into the chopper just as if it were a feather and chop that first. Then you have a "third hand" used to hold the feather flat as well as allowing you to pull it towards yourself against the base. This gives a cleaner, more uniform cut.