Heres a work around to get gliders to release at a way point, although it won't solve getting them to land near where you want, you will have to experiment with the following idea.
Set the aircraft up as normal with way points for the towing ac and a spawn norm fly with set attached from glider at
way point 0
With the towing ac set a
waypoint 1 in front of a g'attack
waypoint 2 the gliders will release at this waypoint.
wp 0 <attach glider
wp 1
wp 2 <gattck
wp 3
wp 4
wp 5 <landing
.