Two similar kernel routes with different metrics on bird 1.6.4

[Andrew]

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?