my site has A LOT categories, like really a lot. Right now im using the "Collapsing Categories" plugin.
Is there a way i can add "pseudo-categories" to show up before the real categories are shown? E.g. the letters of the alphabet: Every (parent-)category that starts with an A will only be shown if you click on the A or the symbol ([+] or a picture) in front of the A. So instead of all your normal categories you would have the complete alphabet before (if you have at least one category starting with each letter of the alphabet) the normal categories are there. 
But the letters of the alphabet themselves dont necessarily have to be interpreted as categories. Perhaps you have a picture of the alphabet or just a normal letter-list above the place where the normal categories are. 
Since i feel that i didnt explain it too well, i made a picture to illuminate the idea.