Step #1
// ------------------------------------------
// Player.cs
// ------------------------------------------
In function Player::use, remove this line:


         messageClient( %this.client, 'MsgCantUsePack', '\c2You can\'t use your pack while piloting.~wfx/misc/misc.error.wav' );


Step #2
// ------------------------------------------
// Vehicle.cs
// ------------------------------------------
Add this function to vehicle.cs:

function fireBooster(%this)
{
   if (!isObject(%this))
      return;
   %veh = %this.getObjectMount();
   if (isObject(%veh))
   {
      if (%veh.getType() & $TypeMasks::VehicleObjectType)
      {
         if (%veh.getMountNodeObject(0) == %this)
         {
            %vdata = %veh.getDataBlock();
            %vec = %this.getVelocity();
            %vec = VectorNormalize(%vec);
            %pct = %veh.getEnergyLevel() / %vdata.maxEnergy;
            %mass = %vdata.mass;
            %amount = %mass * 100 * %pct;
            %veh.setEnergyLevel(0);
            %veh.applyImpulse(%veh.getTransform(), VectorScale(%vec, %amount));
         }
      }
   }
}


Step #3
// ------------------------------------------
// ControlDefaults.cs
// ------------------------------------------
Add this to the top of function ServerCmdStartUseBackpack:

   if (%client.player)
      if (%client.player.isPilot())
         fireBooster(%client.player);