I did it!
Not exactly sure what the format for this should be, so I'll just copy/paste what I did. I copied the line for Standby, changed the right places so they said hibernate, used the same image (since windows uses the same one, it's just a slightly darker color), and changed the windows cmd command to Hibernate. Simple enough. (Tested it too, just in case. It works fine.) Thanks for the help and the push Mouser.
EDIT: Forgot to say what I named the Alias, but I guess people can name it whatever they want. Personally I prefer using "Sleep" since it's shorter and easier to type than "Hibernate".
Hibernate Computer | %ALIASDIR%nircmd.exe qboxcom "Do you want to Hibernate the computer?" "question" Hibernate /ICON=nircmd_icons\Standby.ico