API for 16-bit Cubemap generation

By the moment I use a pack of LUT cubemaps in my project. They have ARGB32 format, but don't use alpha channel at all. I want to convert them to RGB565 format to save some memory and bandwidth.
But by the moment render-to-texture is only solution to achieve this. As I know dithering algorithm works different on different mobile devices, so we get nondetermined result. And we should write a ton of code to achieve it. Also memory layout of these textures can be optimized on rendering-to, but not read-from which can affect performance on sample operations.
It could be better to provide API for such cubemap creation or use simple quantization algorithm for SetPixels or SetPixels32.