I don't think it will work.
Take a look at the setup in profile -- the image on the right side of the picture (vulture_2_launch.png). If that system were stiff, when the rocket fires the plane could slide up right off the rod. But because it's hanging from a tether, it's not stiff. When the rocket fires, the force of the thrust will create a torque that makes the entire structure want to rotate about its center of gravity, which will probably end up someplace inside the truss. The truss is stiff, but that torque will cause a rotation about the one point whose rotation about the axis pointing straight out of the picture is not constrained... which is the where the three tether lines intersect. The entire structure (truss, rod, plane) will probably rotate counterclockwise... in which case the structure may start to rotate before the plane slides off the rod, resulting in the plane coming off at a significantly different angle than intended... or not coming off at all and just spinning around.