blending 2 normal maps to
 

ok people here's a problem.

I made a model (pillar), and made normal map for it.

So now i have file texture node (with normal map), which is conected to bump2D node (file1.outAlpha --> bump2d.bumpValue) which represents normal mapping.

Now, i'd like to add detail normal map, that would be blended with current normal map, but would add details if you come close to it.
Problem is, i tryed to use blend colors node, but output of normal map must be OutAlpha it seems (to be conected to bump2d node), but blend node doesn't have outAlpha, so i dunno how to work this out now.

So, anyone got an idea? In short, how to blend to difrent normal maps to 1 bump2d node?