Finn:

The only way that I know that propagate Peace Lily is by division, the same as you would divide a day lily. If the original plant has lots of growths (all the leaves sprouting from a common point at the soil), you can just reach into the pot & twist off one of the growths at ground level. Try to get some roots as well. Try to grasp the base of the growth right at ground level, or even push your fingers into the dirt a little bit. Then gently rotate the growth back and forth, while gently pulling up. You should end up with an intact growth.

Alternatively, you could take the entire plant out of the pot, and wash the dirt off. Then you could tease one or more growths off the main plant and repot the main plant with fresh potting soil.

Hope that this helps,

Dan