I honestly think (and I maybe wrong, so hopefully the other "vetrens" will keep me honest) that you can't apply as a spouse until you are a spouse, ergo, until after you are married. I realise that your fiancée wants to get her bio appointment done, but you are submitting a legally binding form at the time of application that says you are married, ergo, you can't do that until you are married.
If you submit a form that is honest based on your current situation, they simply won't issue you the visa you are looking for.