Once you have the bottom case off of the XL, turn it over and look in the battery compartment. If you are holding the case so that the writing is oriented is correctly, you will see a small slit in the upper portion of the right edge of the battery compartment. Resting on this slit is the metal catch that holds the volume switch in place. Use a plastic opening tool or something with a fine point and simply lift the metal tab off of the plastic. Turn the bottom case over and you can lift the metal shield off of the underside of the battery compartment (be sure you remove the screws holding the shoulder buttons down first-- the volume buttons share a ribbon cable with the shoulder buttons, which is secured by a couple screws). Using a pair of tweezers, you can lift the volume switch out of the padding under the volume buttons.
Here is a guide on how to remove the shoulder button.
Good luck, let us know how it works out.