I don't have TG2 at hand here, so I'm trying to do this from heart...
Does the visualize normal node has an output? If so you may be able to use 'red to scalar' 'blue to scalar' and 'green to scalar' to split the colours (function node -> convert).
Then build the colour (function node, don't know which type by heart) using the output of the conversion nodes. You can then rebuild the colour in any order you like.
Something along that line.
Then you'd need to create a surface layer, set it's colour to 100% white (1) and set the output of the 'build colour' node as colour function.
Then render your image from top down and you should have your colours right.
Be aware that you only have to figure this out once and that you can save the setup as a clip file for future use/reference.
Does this work?
If so, then I think other people are interested in this too