[flexcoders] how to override a public var, or put it in an interface?

[Sean Clark Hess]

I want to make a class that works with both DataGridColumn and
AdvancedDataGridColumn.  Each of these has a "dataField" property.  I have
subclassed each, and they both implement a common interface.  In the
interface, I have
function set dataField(value:String):void
function get dataField():String

I get the error "Interface method get dataField ... is implemented with an
incompatible signature"

So, if I try to override it in the subclass, I get "incompatible override"

Is there a good way to do this?  I guess I could leave it out of the
interface and cast it as an object to work with dataField, but that's kind
of lame.