Autocomplete - give a readonly list

Autocomplete - give a readonly list

H Guys,

I am using the jquery autocomplete plugin. What I think I may be using the wrong pligin for my needs. I have a form where users register. Obviously each user ID has to be unique. So when they start tyyping I want to five them a readonly list to say These User names are already in use...

if they type "A" I want to give them a notification
These names are already is use
Al
Alan
Alex
Aron

if they type "AL" I want to give them a notification
These names are already is use
Al
Alan
Alex

if they type "Ale" I want to give them a notification
These names are already is use
Alex

But i do not want them to be able to select anything from the list

Is this possible?

Thanks
Alan