You will need the Custom Sounds plugin.

An example of this can be found on the "FBI Qualification" exercise currently available in the community.

Create your voice command WAV files, add them to the Custom Sounds plugin, then save your setup(s) with those desired sound files as the preparatory command. They can also be useful for things like replacing the hit tone on a particular target to "Wrong Target". There are a few exercises that make use of custom sounds in creative ways like this.

Build your exercise using the setup(s) and don't put anything in for the Drill Description or Drill Video URL, as these will be skipped if there is no information to present, and LASR will roll right into the next drill without that normal dialog window, starting with the preparatory command.