how to change OSPF route src ?

Hello, I run bird on centos with multiple ip addresses. what I want to achive might be easily done by running command ip route change default via $def src N.N.N.N where $def is variable and N.N.N.N is local address how can I achive that with bird ? any ospf route magic ? scripting after bird applies routes (I need to pick $def from that script) thanks! Ilya Shipitsin