Thanks folks. Will try and update here. I tried looking at the github source but didn't spend a lot of time in there I was thinking perhaps with a bit of reflection I can change the image view that is displayed on top of the button. Although I managed to show a different image but it looked all wrong. The underlying '+' would simply not go away and would still be visible even if I managed to display another image on top of the button.
Anyways, thanks for your input and great work!
[Edit] The reason I wanted to use reflection was to display fontawesome/material icons using icon fonts.