[Lazarus] How to prevent TComboBox dropdown?

[Vojtěch Čihák]

Hi,
 
I already asked it on forum: http://forum.lazarus.freepascal.org/index.php/topic,25686.msg156312/topicseen.html#new
Don't you know any convenient way?
I tried various ways, so far the best is timer with a very small interval but it's not a very nice solution.
Goal is: clicking left half of the combo will toggle the state while right half will dropdown list. (See the screenshot attached to forum post).
 
Thanks,
 
Vojtěch