Set portions of a Phaser.Image transparent?

[ForgeableSum]

Here's what I'm trying to do:

 

Create multiple layers of images on top of each other. Use a sort of brush tool to set certain pixels of images in one layer transparent so you can see through to images in the layer underneath. I know that this can be accomplished if the images are all bit map data.  However, as my maps are huge, it would not be practical from a performance standpoint to have all these images as bitmap data. One thing I could do is have all the images regular Phaser.Images and convert them to bitmaps when they need to be modified, but before I try that I'd like to find out if I have a better option. 

 

Is there a way I can set portions of an image transparent without the texture of the sprite being a bitmap? Do I have any other options? Appreciate any advice/help.