You could configure the Mac Mini Server to be your network's DMZ. This would mean any incoming traffic would be routed to the server by default. This also means any service you have running on the server would be access-able from outside your local network. (unless you configure the server to do otherwise.)
1. Open AirPort Utility, select your base station, and choose Manual Setup from the Base Station menu, or double-click the base station to open the base station’s configuration in a separate window. Enter the base station password if necessary.
2. Click the Internet button, and then click NAT.
3 Select the “Enable Default Host at” checkbox. The default IP address is 10.0.1.253. I suggest you use that default!
4 Enter the same IP address on the host computer. Also on the host computer, enter the subnet mask (255.255.255.0), router (10.0.1.1), and the DNS server address(es) of your internet service provider.
If you've already set server to a static IP, you could configure the default host to be that IP instead of 10.0.1.253. If you do change the server IP address to 10.0.1.253, after words you would want to reboot the server. if you configured the server to have a FQDNS, you may need to update those settings as well.
-TT