HP 25 Fibonacci sequence in one program step

[Dave Britten]

I've been reading "Mathematical Recreations for the Programmable Calculator", and they have a somewhat humorous puzzle regarding the shortest possible program to produce the Fibonacci sequence.

The HP 25 program they concocted is only a single step, plus the typical GTO 00 to halt and reset the program. This short program does require the user to preload the stack and/or memory prior to running, but then subsequent presses of R/S produce the Fibonacci sequence on the display.

I'm curious if anybody can figure out the silly trick that they used in this book.