No, you can't. Gravity assists require the assisting body (Jupiter) to be moving, relative to the body that needs the assist (Voyager), in the direction the ass

No, you can't. Gravity assists require the assisting body (Jupiter) to be moving, relative to the body that needs the assist (Voyager), in the direction the assisted body wants to go. They have an unfortunate name because it's not just the assisting body's gravity that provides the assist. It's the combination of gravity and velocity. As Voyager nears Jupiter, Jupiter's gravity grabs it. Then, Jupiter's velocity relative to Voyager drags Voyager - that is, transfers energy to it. Without that relative motion, all Voyager's gravity does is add energy on the way in and then remove exactly the same energy on the way out.