Andy, you can kind of make the angle joint mimick an angle spring, by adjusting the Softness and Bias factor. For example, here are the softness and bias factors for the shoulder joint of Krashlander:
float shoulderSoftness = .00001f;
float shoulderBiasFactor = .1f;
Alternatively, you could try to us something like the following from the Box2D manual. This snippet of code uses the revolute joint motor to mimic and angle joint.
float32 angleError = myJoint->GetJointAngle() - angleTarget;
float32 gain = 0.1f;
myJoint->SetMotorSpeed(-gain * angleError);
Finally, you might just look at the angle spring code from the old Farseer source and try to port it to the new engine. I can't imagine it's too complicated. Haven't looked at it, though.