if you haven't launched yet, why not change your name? I understand that there are costs involved, but did you quantify those costs and see if it's possible or not? You don't have to redo everything at once.
If I were to take on the project myself, I would be willing to put in more cash for that purpose. But I worry about my cofounders claim to half of the business, and risking more of my own money when he technically has the right to half of the reward.