Using a padding-like style to position text in a button. Add eventListeners to View object instead of Button.

button_text.js

$.button_view.addEventListener('click', function(e){
  alert("Button Clicked");
});

button_text.tss

"#button_view" : {
  width : "100dp",
  height : "100dp",
}
"#button" : {
  width : Ti.UI.FILL,
  height : Ti.UI.FILL,
}
"#button_label" : {
  textAlign : 'center',
  left : "10dp",
  width : Ti.UI.FILL,
  height : Ti.UI.FILL,
}

button_text.xml

<Alloy>
  <Window>
    <View id="button_view">
      <Button id="button" />
      <Label id="button_label">Label</Label>
    </View>
  </Window>
</Alloy>