lba48 partition modes: 

0 = standard partitions 
1 = F: gets all (Default)
2 = F: up to 137gb, G: gets rest
3 = F: up to 137gb, no G:

You have to patch 0,1,2 or 3 value at offset 0x1b04 (if you wanna hex dit manually)

However there are tools for lba48 patching and ini file creation - they can be found here:

http://home.alltel.net/nghtshd/x2ool.html
http://x-projects.xbox-scene.com/