Okay, I had to figure this out myself but it has worked for me and it was an easy fix:

1) Go to your installation directory (should be something like C:\GOG Games\Ultima VII - Complete\SERPENT)
2) Find the file "dosboxSERPENT_single.conf" and open it with word pad.

[It should look like the following]

[autoexec]
@echo off
mount C "..\SERPENT"
cls
c:
serpent.com

exit

3) add the word 'manimal' to the line serpent.com
[so it now looks like this]

[autoexec]
@echo off
mount C "..\SERPENT"
cls
c:
serpent.com manimal

exit

4) Save and close. Start your game up and F2 should now open the debug menu. (see location.jpg [attached] for screens)

As I have already stated, I found this out for myself and have no idea (though I seriously doubt on all accounts of what knowledge of computers I do have) if this method will have any adverse effects.

This should also work (with the appropriate command line change) for getting the "jive" intro - an easter egg of sorts - to play.