[CentOS] per port ip routing -- possible?

Hello,

I have a customer who has two Internet connections, cable and DSL, where the cable is much faster than the DSL connection. Is it possible in CentOS 4.2 to use the "ip route" command to direct certain outbound traffic over the faster connection, say http(s) requests? Web searches turn up solutions where NAT is involved, but this guy isn't using NAT. Example configs that show how to load balance multiple connections and ensure symmetric routing all work great, but I don't an example of per-port routing.

Any pointers or example commands would be greatly appreciated.

Jack