I'm at a bit of a loss here - as anything to 'train' means a climber to me, and they don't stay at 3'. However, a few alternative ideas for you. Facing south - how about a lavender hedge? Santolina? Small varieties of cistus? You could also interplant with the new 'Boulevard' clematis to flower in the summer, as long as you shade their roots. They're not evergreen, but would look great. Then there are patio roses, as another thought for you.