I had a HP that I could mount the negative to a piece of dark card stock, position it under the transparency light and scan. Can I make my own mount for negatives to scan odd sizes with the V600?

This scanner has inserts to put film and slides in for scanning. I believe you could probably invent something to do your own custom positioning, but know that the width of the transparency light seems to be somewhere between 2 and 3 inches -- I can't get my 3"x5" transparencies in a single pass. I will note that I have been moderately successful scanning larger transparencies on this scanner by telling the software that I am scanning a reflective (like paper) document, and simply placing the transparency on the scanner bed, and then putting a mirror, reflective side down, on top of the film. If you have a big enough, perfect enough mirror, you can get a decent quality scan of even a letter-size negative. That would lend itself to your custom mount pretty well, I'd think.