Adjust textarea height to make room for keyboard

I'm building a Alloy based app for both iOS and Android.

I have a modal window with just an textarea in it and I'm trying to make the textarea fill out the entire space left (minus my header off course) when the keyboard is open. It would be easy just setting a hard value for iOS devices but then Android comes along...

Can it be done?

xml

<Alloy>
    <Window id="confessWindow">
        <Require src="header" type="view"></Require>
    <TextArea id="confession" suppressReturn="false"></TextArea>
    </Window>
</Alloy>

"#confession":{
    top:"55dp",
    width:"100%",
    height:Ti.UI.FILL
    }
}