Further to my previous post, if you really want to make this user friendly then add the Focus Bracketing override menu items to the CHDK User Menu and have it be the first thing that opens when you press the <ALT> key. For example, this is what I currently see immediately upon pressing the <ALT> key on my A1200 :

That lets me immediately adjust my bracketing settings without having to open the main CHDK menu and navigate all the way through to the sub-sub menu.
Details on how to do all of this are here :
User Menu Make sure to read the part where it descibes
On Direct mode