There have been a few questions posted on this topic, so I thought I would share how I did it.
The wireless controller uses Torx-8, with a security post in the middle. I went out and bought a 100 pc security bit set. You can get em off eBay for about $15.
Taking out the T8security bit, you will notice you can get every screw out of the controller, except for the two in the tips of the handles. (There are 5 others, one in each handle, one on either side of the battery pack and 1 under the barcode under the battery pack)
As for the two in the handles, the bit simply doesn't fit.
I modified my T8 bit so that it fits. Here's my modified bit next to a stock one.
The hexagonal part of the bit is about twice as long as needs to be...if you put it into a bit driver, you will notice quite a bit of it sticks up and doesn't allow you to take screws out of your controller.
Put the bit into a bench vise, if you have one. Clamp it perfectly vertical, nice and tight, with about 1/4" of the hexagonal part above the vise.
Using a metal file, work your way around, taking care not to nick the tip, as it's pretty small, and damage could cause it to strip. You don't have to take much off, just enough that it will fit.
Success! The bit can now recess into the controller enough to fit the screws. Happy modding!