How can you do this stupid cheat?

Im playin perfect dark on my xbox 360 and you are supposed to beat the G5 building mission in 1 minute 40 seconds to unlock the cloaking device.Well this is impossible. I know about the spycam trick, but its still impossible. It takes me 1:40 to get past the guards. Ive tried it 195 times so far and my best time is 2:45 seconds. Tips? Like where throw this piece of trash of an impossible videogame?