How can I make GAP compute Aut(G) for small groups G in a simple
and/or efficient way?
                       Peter Jipsen

I forgot to mention that you need to make sure that the
representaion you take has a point stabilizer that is
invariant under Aut(G). This will off course be guaranteed
if for some reason you know that there is a unique G-conjugacy class
of that isomorphism type.
Kay Magaard