Code:

init

{
  _unit = _x;
  if("instruct" == vehiclevarname player) then {_x addAction ["Teleport", "teleport_enable_once.sqf"]};
  }foreach allUnits;

Code:

teleport_enable_once
_stud = _this select 0;
_gen = _this select 1;
_id = _this select 2;

_stud removeAction _id;

_cancel_action = if("instruct" == vehiclevarname player) then {_gen addAction ["Cancel teleport", "teleport_cancel.sqf"];};

onmapsingleclick format["%2 setpos _pos; onmapsingleclick ''; %2 removeAction %1; %2 addAction [""Teleport"", ""teleport_enable_once.sqf""]; true;", _cancel_action, _stud];

player sidechat format["Click on map to teleport there, or use cancel teleport action"];

Code:

teleport_cancel

_stud = _this select 0;
_gen = _this select 1;
_id = _this select 2;

_stud removeAction _id;
if("instruct" == vehiclevarname player) then {_gen addAction ["Teleport", "teleport_enable_once.sqf"];};
onmapsingleclick '';

player sidechat format["Teleport canceled"];

all you should have to do is name the unit the instructor wiill be as instruct