Obviously there is some discretion available to the application processor to allow applications outside the rules. For example my partner (on a WHM visa) switched in-country to an unmarried partner visa based on my in-country switch (WHM->WP) earlier this year.
Work Permits also confirmed to me prior to our application that this was not possible. If you don't mind the fee and the potential that it may be wasted should your application be denied, you might just want to try it.
Alternatively I'm sure the UK embassy in NZ has a same day visa approval process should your partner want to return home to make the application.
PS: Facts that may or may not have contributed to the plain sailing of our application outside the rules:
- My partner's application for FLR as an unmarried partner was made on the same form as my FLR application as a IED holder.
- The application was submitted by a solicitor.
- The application's documentary evidence of the relationship was extensive and very well organised.