Share internet between two NIC's (mountain lion server)

Ok I give up 🙂 I've browsed the internet for a day looking for a solution to my problem without any luck.

I run Os X mountain lion server and I'm suppriced about what apple think that a sever edition should be able to do. I'm not running a big network but i've already feel that this server software is a little bit small for my needs.

To the problem:

I have two networks on different subnets that is connected to my Osx server on two ethernet interfaceses.

One network has a router on the other end and is connected to the internet. The other network has no router and needs to be connected to the internet trough my Osx server.

We all know about the bug that disables NAT and DHCP when you start internet sharing. So what to do?

Changing subnets or getting another router is not an option.