Utilize two gateways on the same network same interface with load balancing

The only way to have multiple default gateways that I know of is to utilize the methodology shown here: http://lartc.org/howto/lartc.rpdb.multiple-links.html. However one modification I would recommend over this methodology is instead of putting things in /etc/rc.local, store them in network route/rule files (again, this is assuming red hat so YMMV - /etc/sysconfig/network-scripts/route- and /etc/sysconfig/network-scripts/rule-.

To get a single interface to be seen as two interfaces, you could create subinterfaces by following the methodology shown here: http://linux-101.org/howto/create-sub-interfaces-centos-and-redhat