Two similar kernel routes with different metrics on bird 1.6.4

Hi all. I have two default kernel routes with different metrics (for failover, when first gateway becomes unreachable - all traffic is switched to second gw). I want to pipe it to other kernel table to gracefully handle connections to second IP. Unfortunatelly, I can't force bird to learn route with higher metric - bird just ignores it. Option 'merge paths' does nothing in that case. Import filter doesn't help - it seems like route is dropped somewhere in protocol, before passing to filter. How can I force bird to learn route with higher metric?