If this can be changed into a spherical map you can, well, map it to the planet in a spherical way thru an image map shader, and use as a mask (output to mask input of surface shader). White for the oceans, obviously, and if you inversely mask a surface shader, you can add all sorts of textures and displacements as a child of that surface layer, building up your planet.
Perhaps you can add your tgd here, so we can check it out.
EDIT: Even in a simple setup it works with a Y projection, but for nicer continents you have to blur the image.