You just need 2 controllers for this. Start an Infiltration match on the first map with no time limit and however many wins you want. Pick the phase cannon as your starting weapon.
Bring your first controller guy down on the ground so you can shoot across to the other side. Now with your second controller come down stop for a second and then run into your goal and then when the mimic comes kill the mimic and the second controller player with the same shot.
If you watch my video starting at 4:00 you can see me doing this.