Terminator was nice enough to writeup this newspost for me. He says:

A few days ago, striderdude posted a thread showing the capture of the spawned Plasma Rifle at the end of the Outskirts hallway. This was done with mods, however, and the guys in the Halo 2 Campaign forum were challenged to snatch the weapon without any special modifications. Our KORHAL threw out the idea to use a soda machine to launch through the tunnle fast enough to grab it. It was then, after trial and error, Enanito swooped in and grabed the prize for himself. Most impressive work, great job to all of you!