XCFloresX photography does an awesome job of this mod on a youtube video. Watch his video first!
My instructions are just a specific case for my camera and the 3.5mm jack I chose to use. I have the Asian model not the Rebel.
Make sure you get all the screws out before you remove the back case. The back case comes off quite easy. My camera had a screw hiding below a sticker.
When you take the back cover off be careful not to damage the ribbon attached to the circuit board.
Small Philips screwdriver - make sure it fits properly in the head, these little screw heads will strip out easily.
Small Flat screwdriver - to pry off the back cover.
Hot Knife or a small saw, something cut plastic
Small file or Dremel
3.5 or 2.5 2 pole audio jack
Step 1: Placing the Jack
Step 2: Soldering the Jack
And I also bent down the jack tabs to ensue the back case would fit back on.
The back cover has a metal shield inside it so I added a small piece of electrical tape to ensure the jack contacts didn't short out.
Step 3: Back cover material removal.
I used a hot knife to remove the plastic and then a grinder to remove small amount of metal required.
NOTE: Try not to get any small bits of plastic or metal into the body of your camera. Nothing good can come from that.