Do you know anything about growing on a Christmas Lily plant once it has finished flowering?

As happens nearly every Christmas, I was given a wonderful specimen of a Christmas Lily plant, just over a metre high. The flowers have now died and I would like to plant it out into the garden where it will hopefully continue flowering each year. I hope there is someone out there who can advise me. It might help to know I live in NZ, enjoy a temperate climate, and only very occasional frosts. One of the things I would like to know is whether to cut the single stem back, and if so how much to trim it by.