ip route add dst-address=10.0.0.0/24 gateway=ether1
Note that this is a particularly bad example for the requested feature, giving an ethernet interface as the gateway. If this feature is implemented at all then it should be implemented for point-to-point interfaces only.
Why is using this with ethernet (or any broadcast / shared-media interface type for that matter) a bad idea? Well, if no next-hop IP address is given but only an interface (like in the example), then there is no way a MAC address can be resolved (using ARP), because without a next-hop IP address, for what IP address would you ARP for? So the only possible way to transfer the packet is to send it out of the interface with a MAC layer broadcast destination address (MAC FF:FF:FF:FF:FF:FF). This will make every
packet a broadcast and flood all your switch ports with every packet, as far as ethernet is concerned.
The only situation I would ever find this acceptable is when the physical topology is strictly point-to-point, e.g. a crossover cable between two ethernet devices and nothing else.
On point-to-point interfaces it's a nice feature, though.