A grenade jump to the room across the shaft.
On April 4, 2002, bonk challenged the HBO Forum to get into a small room across the Silent Cartographer main shaft from the platform that triggers the 'Shafted' cutscene. The next day, xbill reported that he'd gotten a Warthog in there... and 3 hours later, he managed to get himself in there. These pictures and movies document the feats. (The first movie shows the warthog launch - the second shows the player launch.)