alias ip and natd with ipfw fwd

[. at babolo.ru]

> Can anybody please help with problem.
> Using natd and ipfw and trying to fwd packets to a non-default router 
> out the same interface.
> Currently using alias for the second ip, but it doesn't seem to be 
> working for some some reason I'm missing. Would clone maybe work?
> Any advice would be appreciated.
ipfw rules, ifconfig -a and natd options need
to be demonstrated.