I don't have an XL2, but it looks like there's a setting for "SHOE" on the audio controls on the side. It looks like you'll also have to switch to 32kHz/12 bit audio by going through the menu.
Here's a page with more information: http://kbsupport.cusa.canon.com/system/selfservice.controller?CONFIGURATION=1011&PARTITION_ID=1&secureFlag=false&TIMEZONE_OFFSET=&CMD=VIEW_ARTICLE&ARTICLE_ID=3870
Here, also, is a similar thread on dvinfo: http://www.dvinfo.net/forum/canon-xl-gl-series-dv-camcorders/61803-dm-50-xl2.html
