Bumping rules are different depending on what region you are in. But I would venture to say you probably have no bumping rights in this situation. Almost all contract language that allows bumping, requires that you are displaced from your current work.
But...... If they officially make you an ODC clerk. You would then have more seniority than this other guy, and if your supervisor wanted to send one of you to go do other work, like loading or unloading, he would have to honor the rules of seniority and send the lowest seniority person.
Im pretty sure in our last contract, there was a special provision to merge clerical and package handler seniority lists. So UPS can no longer discriminate ODC seniority vs package handler seniority. But again, this may have been locally in a supplement or rider just for my region. Your best bet will be to ask your shop steward and/or read your supplement and rider yourself to find the info you are looking for.