Did you try the userlist in "searchmode" ? Since that "view" opens the search form at once, it might be a good start. Although there is an additional URL param for the searchmode, I assume that it does not "trigger" the searchbutton and form display directly. The important function or task seems to be the "userlist". Also jQuery is involved here...
The only way without core edits might be a addional jQuery/Script that triggers the same action on the regular URL... or on that particular menuItem.