I think you'd have to break the wing into a number of rigid body elements with joints between them to approximate the flexible and elastic properties. The joint properties plus actuator controllers property tuned could do the physics, or a separate model of a wing could generate the position of every rigid body and the actuators would be driven to try to match that.
Other than that I'm working on a simulation package that wraps the bullet physics engine: https://github.com/lucasw/simple_sim_ros , bullet supports soft bodies and I'll add support for those eventually. Try out the bullet demo applications and see if the soft bodies might work for you, there are volumetric kinds (with internal 'struts') and others which are more like balloons (only a surface, which is easier to import from a mesh).
Update
simple_sim_ros main branch now supports bullet soft bodies
Also there is work towards support in gazebo: https://bitbucket.org/osrf/gazebo/iss...