It sounds like you need to expose your Mac directly to the Internet in order for this to work. In the sense of routers and firewalls, this is called a DMZ (demilitarized zone).
On my Linksys router’s web admin screen, there is an advanced tab that leads to a tab that says DMZ Host. From there, I can enter the private IP address of any of my computers on the LAN and have it exposed directly to the Internet. Obviously, the admin interface for your Netgear router will be different, but look for something like that in the helpfile or in the admin app.
Of course, while you leave your Mac in the DMZ, you give up a lot of the protection your router’s firewall was providing. It’s a hassle to move your Mac in and out of the DMZ, but unless you are sure you are keeping the security patches up to date and there isn’t anything on the Mac you wouldn’t mind someone else getting access to, you probably don’t want to leave it out there all the time. Of course, I suspect most people with broadband have a single computer hooked directly to their DSL or cable modem, so you won’t be the only target, by any means.