By default, you cannot plot minimum principle strain or extension strain with RS2. Using the Define User Data option in the Data menu, though, you can define functions of stress and strain.
For example, you can define a user data function called e3, which plots the induced minimum principle strain using the equation:
((exx+eyy)/2.0) - sqrt((exy/2.0)^2.0 + (((exx-eyy)/2.0)^2.0))
This is the plane strain equation for minimum principle strain. These are induced strains and do not include the locked in strain due to the insitu stresses. If you want to define Stacey's equation for extensional strain, you could also do this using the User Data option.