I'm curious as to why you are asking. SME server usually operates as a peripheral node on the Internet, and has no need for dynamic routing. What problem are you trying to solve?
Actually, there is no problem with SME server. Now having played with it in gateway mode I see I can add "test" subnet as local networks and packets will be routed to it.
I was thinking gateway mode would be similar to Smoothwall, where Smoothwall does not know about other subnets and as such routes packets destined for them out the default gateway instead.