Flex Mobile: preventing back button from exiting app

I'm developing a Flex Mobile application for some android tablet and until now I've been unable to prevent the Back Button from leaving the application. I still want it's regular functionality, it's just that I don't want it to exit the app. I want the user to do this manually.

Any ideas on how to achieve this? Maybe by catching some event? Any help will be greatly appreciated.

Regards,

Sebastián

Here is how I handle it:

<?xml version="1.0" encoding="utf-8"?>
<s:View xmlns:fx="http://ns.adobe.com/mxml/2009" 
        xmlns:s="library://ns.adobe.com/flex/spark"
        initialize="init()"
        viewActivate="activate(event)"
        viewDeactivate="deactivate(event)">

<fx:Declarations>
    <fx:Component className="ConfirmExit">
        <s:Callout 
            horizontalPosition="middle"
            verticalPosition="middle">
            <s:VGroup width="100%">

                <s:Label text="Really quit?" />

                <s:HGroup width="100%">

                    <s:Button label="Yes"
                              click="close(true)" />
                    <s:Button label="No"
                              click="close(false)" />
                </s:HGroup>
            </s:VGroup>
        </s:Callout>        
    </fx:Component>
</fx:Declarations>

<fx:Script>
    <![CDATA[
        import spark.events.ViewNavigatorEvent;

        private function activate(event:ViewNavigatorEvent):void {
            // add exit confirmation dialog - Samsung Apps requirement
            if (Capabilities.version.indexOf('AND') >= 0 &&
                Capabilities.manufacturer.search(/Samsung/i) >= 0) {
                _confirmExit.addEventListener(PopUpEvent.CLOSE, handleLeaveCallback, false, 0, true);
                stage.addEventListener(KeyboardEvent.KEY_UP, handleKeyUp, false, 1, true);
            } 
        }

        private function deactivate(event:ViewNavigatorEvent):void {
            _confirmExit.removeEventListener(PopUpEvent.CLOSE, handleLeaveCallback);
            stage.removeEventListener(KeyboardEvent.KEY_UP, handleKeyUp);
        }

        private function handleKeyUp(event:KeyboardEvent):void {
            if (event.keyCode == Keyboard.BACK /* && navigator.length == 1 */) {
                _confirmExit.open(this, true);
                // event.preventDefault();
            }
        }

        private function handleLeaveCallback(event:PopUpEvent):void {
            if (!event.commit)
                return;

            try {
                NativeApplication.nativeApplication.exit();
            } catch (e:Error) {
            }
        }

I.e. don't call any base class methods and use the priority of 1 here:

stage.addEventListener(KeyboardEvent.KEY_UP, handleKeyUp, false, 1, true);