Port forward SSL VPN 10443

Hi, I have a number of remote users using the SSL VPN via port 10443. I would like to change this to port 443 (which I know can be done easily) as when our guys are working from client offices the 10443 port is usually blocked. Thing is, I want to have both 443 and 10443 available for SSL VPN so that users already set up to run on 10443 don' t get broken in the changeover. Is there a way to port forward 10443 to 443 on the external interface of the fortigate? Or, if this is not possible, can I set up a second IP on the external interface and port forward from one IP to the next? Cheers, AJ