Dynamically accessing static variable between two classes: cutom key pressing

programming flash
1

End point I am trying to allow users to define their own key preferences.
My approach currently is as follows:

I have a .as called ‘Keys’. It has some boolean variables corresponding to a set of keys and allows global access to the key press status.
eg

 
package
{
     public class Keys
{
      public static var a:Boolean = false;
     //etc
}
}

I also have a .as called ‘KeyWatcher’.
It handles all the listeners for key presses etc.
It has a peice of code that does not work:

 
 protected function keyPressHandler(event:KeyboardEvent):void
 {
  var Keys_a:String = 'Keys.a';

  switch(event.charCode)
  {
   case 97:
   Boolean(Keys_a) = true; // error 1105: Target of assignment must be a reference value.
   break;   
  }

I know why I am getting the 1105 error, I just put this in as an example to try and convey what I was trying to do.

I want to keep the reference as a variable (eg Keys_a) so I can reasign its target (eg Keys_a = ‘Keys.b’)

[COLOR=black][FONT=Verdana]I apologise for the convoluted status of my query but I am not really sure what approach I should be taking. [/FONT][/COLOR]

thanks for taking the time to consider my question.