Don't jump off the ground, forward momentum will be lost. Jump as hard as you can without sacrificing forward momentum. There are differences between the pole vault jump and the long jump jump. As soon as you body has lengthened, start to swing. If driving is jumping hard and stretching your body as you leave the ground, do it.
Coach stands behind the vaulter.
Coach follow the vaulter - at takeoff, coach places his hands on the vaulters back on his sholder blades and pushes the vaulter forward and up slightly, then guides the vaulter back down onto the runway. On takeoff, the vaulter should concentrate on keeping his body vertical with his bottom hand over his head as described above. Note that since the coach is holding the vaulter, it will be difficult for him to see if the vaulter is doing it right - maybe 2 coaches are needed here. Use a short pole with a low handgrip so that the vaulter can land in the middle of the pit. This drill will require doing the pole drop and transition correctly also.