Some of the avatar files have a male shape included. Others appear to NOT have the separate male shape. You can also import a male shape to Blender by exporting one from SL. See Second Life Mesh Clothes Blender 2.6 Setup 2012 Tutorial for information on how to export from Second Life® and details on which shapes are what.
This tutorial is about working with Blender 2.63a shape keys to get the male shape. It will also give you some idea of how the Alternate or Redpoly Deformer can work.
If you make petites or giants, getting a copy of the male model that is well weighted is important. If you have tried exporting the male model as a mesh for use in SL, you likely ran into problems. This tutorial will help with exporting the male model.