Hi Chalukya,
Though not sure, still I guess all the values in a dropdown are pre-existing or if we use dynamic properties to update the dropdown we can know atleast what could be it's length.May be that's the reason expand options are not available.
But if you want to expand it you can do so a bit of scripting.
When we select something from the dropdown through change event we can get the vairable length. If the variable/item length is greater than a particular value then we can expand the dropdown.
In the change event of the dropdown :
You have to use FormCalc if you want to use Len otherwise you can use an array in javascript.
if(Len($event.change)) > 10
{
this.w = "10inch";
}
Thanks,
Bibhu.