On a server while playing Karkand with Friendly Fire off, play as the Spec Ops kit. Walk over to the big building overlooking the train accident flag. Place all five of your C4 charges on the ground about ten feet from the building and run over onto them. When you are about one foot past the charges, detonate them while still running. This should give you enough momentum to launch yourself onto the roof. From the roof, find the slightly raised roof access door and get into a prone position. You should pass under the slightly elevated ground and then be able to fire on the train accident flag without the enemy being able to see you.