I've created a large file full of noise that replaces the Mad Warrior's helm. While running GeDoSaTo and using it to replace textures, the game will freeze for roughly 1 second or so when the Mad Warrior spawns. (I have an SSD, it may be longer for you guys.) Feel free to resize the image if it takes too long to load. I've made a version for both SSD and HDD users that should hopefully make the stutter noticeable but not annoyingly so, after all farming is about speed. You should use the SSD version first. If the SSD version takes too long to load use the HDD version. I don't own a HDD so I can't really test how fast or slow it will load it, I can only estimate.
Basically what happens is when you farm the Mad Warrior, you rest at a bonfire and check your memory usage and see if it goes up. It usually goes up by 13k or so, but I've had so many fluctuations that it's very hard to tell if he actually spawned. What I did was make a file full of noise so that when resting and reresting at a bonfire, your game will stutter a bit when he does load in. Alternatively, this makes it easier to check the memory usage, using this mod the memory usage will go up by ~20 mb instead of ~13. It's not a very effective difference, but when I used a much bigger file that increased the memory load by about 60mb the game would freeze for roughly 40 seconds to load the memory, and no one wants to wait that long. As it is, you should definitely be able to tell when he spawns without even needing the task manager now.
GeDoSaTo is required: http://blog.metaclassofnil.com/?tag=gedosato
More info:
http://www.reddit.com/r/DarkSouls2/comments/242mtb/efficient_mad_warrior_farming_on_pc/
http://www.reddit.com/r/DarkSouls2/comments/259vdm/farming_mad_warrior_pc_memory_usage_and_the_aged/