There is a cheat and a tip on The Streets that I know of. First of all the tip, in the beta base as you walk in on the left hand side are 3 sets of boxes, go to the one facing the stairs.
Crouch down behind the target man, go close to the wall but still being able to move closer, if you cover and go up so your looking at the man with the stairs on the right.
You should also be aiming on your players right hand side, not his left; your gun should be pointing at the man but your crosshairs on the stairs
Now you can shoot through the man without being shot.

Second is the cheat, host a game and tell everyone to get motion sensors and tell them to meet in the left building (from the alpha base point of view).
Go to the balcony where your looking directly at the beta base top left window and there is a box, get everyone to put their motion sensors on the front middle of the box, not the side you are facing when you walk in.
After a while when there is a solid red beam run directly at the beam you should then glitch onto the box
Now turn left and follow the wall till you get to the rappel, take a bit of a run up and dodge just to the right of the rappel and if done well you should land on a rail.
Follow this rail and you should drop down with a roof above you.
Turn right and follow the grey floor after about 10 or 20 seconds you will see a wall on your right which will have a cool picture of a silhouette of a gun man on it and you can also jump off the edge off the map.