Putting 1/4 round at the back of a tread where the risers meet it is NOT a good idea. First of all, you are just covering up a badly built stair and second of all it can be dangerous. It will not look good. My advice is to find a local stair company that specializes in stair work and get someone to inspect the stairs and give you a "free" quote on the best way to get you what you want. If you are in the Atlanta, Charlotte or Raleigh are we can help you with that. If not close, I can find you a reputable stair company in your area that may be able to help you. Just email me if you need help. sfoster@sumstairs.com