Unfortunately, no. There is no way to use the email forwarding independently from the web forwarding because your domain's name servers also receive and direct email requests along with web requests for your domain. By using our web forwarding services, you are using our name servers, so we are able to forward mail to you. But if you decide to use someone else's name servers, we will not be able to set your email settings. You will have to ask the maintainer of your name servers to set the email forwarding for you in this case.