Question: OSPF path selection based on streams

OSPF Routing question: Traffic path manipulation

n1 ------- ------- ------- n2 -----| R1 |------| R2 |------| R3 |------ -----| |------| |------| |------ n2 ------- ------- ------- n4

I have 3 OSPF routers. There are two interconnections between each set as shown in the diagram. Traffic is being sent from n1-->n2 and from n2-->n4. Both streams are folowing the OSPF best path between R1, R2, and R3. The problem is that I want some of the traffic to flow through the top links and the other streams to flow through the bottom links (different paths) without the use of ecmp.

I'm wondering what is the best way to accomplish this? Would a route policy work such that the policy selects the OSPF next hop for some streams on one set of links while the policy selects the other next hop for the other set of streams? Is there another way to do it?

Thanks,

- Daniel