Plugins aren't called for the 'prepare' stage

It appears that the plugins aren't being called for the prepare stage, only the switch stage.

$ disper --version
disper 0.3.1

$ disper --plugins=debug -e
Disper hook environment for stage: switch
  DISPER_BB_RESOLUTION=2320x1050
  DISPER_VERSION=0.3.1
  DISPER_DISPLAYS=DFP_0 CRT_0
  DISPER_LOG_LEVEL=30
  DISPER_RESOLUTION_CRT_0=640x480
  DISPER_STAGE=switch
  DISPER_LAYOUT=right
  DISPER_RESOLUTION_DFP_0=1680x1050

I ask because I wanted to write my own hook that uses it, but it appears the event just plain doesn't exist.