I've been using the strat from Munkki's run of leaving the two NPC's outside and syringe clipping through the door and discovered that if you leave the NPC's close enough to the outside of the door, when you teleport to them for the syringe animation it instantly takes you to the next level.
You just have to make sure that you take Pierce's flamethrower between your own syringe animation and the one on the NPC.
I haven't done much testing with it, but after accidentally getting it to happen I tried again and got it first try, so it doesn't seem too hard to do. If you don't get it right then you can just continue with using Pierce to clip through the door.
Looking at the segmented run by Zero that Munkki uploaded, it looks like Zero accidentally got this to work as well... lol
He also mentioned it in one of his posts on SDA.
"In Segment 3 the level ends suddenly. -I don't know why, but when I recorded it, it ends suddenly. <-- Is that allowed?"
