Randomly ordered GUIs sandwiched between fixed order GUI.

I would like to accomplish something like the following. Please note that these GUIs were all originally made with GUIDE:

Sand-wiched between gui_intro and gui_end are a series of interconnected GUIs that appear in a random order:

1. gui_intro

- After pressing the appropriate button in this GUI, it leads to one of the GUI's below (randomly selected):

2. [gui1, gui2, gui3, gui4, gui5, gui6, gui7, gui8, gui9, gui10, gui11, gui12, gui13, gui14]

- These GUI each have a button to move onto the next GUI in the set

- Each GUI must appear a total of one time and each appears one at a time.

- The order must be random.

- The last GUI that appears in this set must lead the user to the last gui (gui_end) from pushing the appropriate button:

3. gui_end

How may I accomplish this? Input would be much appreciated.