trouble setting up routing

I'm trying to setup a multi-homed host with three network interfaces.  I
would like outbound traffic to share the three interfaces equally but
I'm having trouble making that happen.  I'd also like to do this more or
less statically.

For application reasons the three interfaces are on separate IP
networks.  Two of them are logical networks, i.e., they share the same
physical path.  Thus, there are only two physical networks.

Each of these networks has a path that continues to the Internet, which
is why I want to share them on the outbound side.

I know I can not do this strictly statically since you can only have one
"default" route.  The networks do not have a routing daemon available.

I've been trying to use in.routed with "-q", but I only seem to get
traffic going out one interface (except for the traffic for the network
on the interface, of course).

Has anyone done this before?  Is it even possible?  Am I missing
something obvious?

Thanks for any help,

Jim