[flexcoders] Binding to a custom method: possible?

[ben.clinkinbeard]

There was a similar question asked here recently but my needs are
different so I am starting a new thread. My needs are as follows: I
have a ComboBox whose enabled state needs to be determined by several
factors, thus the need for a custom method. The problem is that this
doesn't seem to work, no matter how I try it. Am I missing something
or is this just not possible (meaning I have to set a property and
bind to that)? Fake sample code below:

[Bindable]
private function isEnabled():Boolean
{
   if(conditionA)
   {
      if(conditionB)
      {
         return true;
      }
      else
      {
         return false;
      }
   }
}

<mx:ComboBox id="cb" enabled="{isEnabled()}"/>


Thanks,
Ben