Making the Blaster Launcher psi-dependent would be lore-unfriendly, since psionically weak aliens use them too. However, I really like paying with additional TUs for every waypoint used, as described by Moriarty. Therefore, each shot would take a certain base number of TUs (probably similar to a rocket launcher in aimed mode) and whatever extra TUs you want to burn on waypoints.
Actually it might be good if each consecutive waypoint took more TUs than the previous one, putting some limit on crazy stunts with blaster bombs.