How about instead of making it an option, make it optional? E.g. allow empty values for the second password field, but if its not empty, check it matches.
I'll exlpain why it'll be useful for me.. Whenever I'm logging into existing accounts, I prefer not to have a confirmation.. (btw, I store my master in the memory). If my login works, then I know my master password was correct and can freely create new accounts on other sites without have to re-type the master password. However, if the first thing I do in a browsing session is create a new account, then I'd like the peace of mind of having the master password confirmed.
For the time being, if I ever want to skip the confirmation I just open up passwordmaker and type the password in there.