You must be persistent, but I think you can speed up the process if you can show him that you are a trusted and active member of the community. I believe that he performs some basic checks when he gets the time, and if you have a blog or Github account that he can briefly check, I think this will speed up the process.
However, this is not entirely necessary. For example, I did not have an online presence when I first asked for an account, and it still endorsed me anyway. Just hold on and he will answer.