Didn't tested it but it looks like you have to do the following:
ModTextureAnimation animatedTex = new ModTextureAnimation(1 /* The Icon ID*/, 1, CommonProxy.TERRAIN_PNG /* Your Texture file */, img /* The Image with the custom animations */, 1 /* the tick count between two "frames" of the animation */);
animatedTex.setup();
animatedTex.bindImage(Minecraft.getMinecraft().renderEngine);