I think I follow your question. I sometimes will take a recently developed negative and hold it emulsion side up over a dark background (a dark tray or just a dark corner of the darkroom) and will see a "positive". It works well with thin negatives, and poorly or not at all with dense ones. If your negs are thin you could certainly experiment with the negative emulsion side up over dark board and see if a positive image is visible - you have to be at the right angle as well. If it works then carry on the experiment with jappaned metal to see if that gives you more definition. I'm not sure if a space between the neg and the background would be needed. Mount in a shadow box maybe. If the negative is dense, I just don't think it will work.
Let us know how the results pan out.