Just trying to help people with a perfectly acceptable solution.
Kill a Corpser on Hardcore
You've played through on Casual getting all the COG's by now right?
from the start Menu - Campaign - Single Player - Load Previous Chapter - Act 3 - Angry Titan
Takes you immediately where you wanna be.
Simply be cool, fire at the beasty's belly when it's legs are in the air and keep pushing fwd's.
It has no real offence (apart from the Retches but you'll be done by then) so keep cool and keep pushing.
The Corpser will back off to the platform
at which point you shoot the left and right (blueish) ground latches that hold the platform steady.
Good Luck (but you wont need it)