Go get any reasonable SV lawyer to have him sign back his stock to the company and then cancel the shares. You can make him an advisor and give him a grant to recognize him for his early efforts.

You will need all the equity you can as you build your company and being nice now giving a big chunk to a non-participating founder will make you bitter later.

If you don't think it will, then let him keep his ~25% vested. He'll be diluted, just like you and everyone else as you raise more.