Hi,
As far as I know, it is not possible to transform BGP routes (with gateway) into device routes in the bird itself. But may be somebody else knows the trick.
From my point of view you can consider such options:
- patch bird with custom protocol, which will do the thing
- add some fictional remote address to the device and use it as a gateway, for L3 device arp should not be used, so it should not be actually configured on the remote side
- export routes to some other kernel table and run some software that monitors this table (through netlink for example) and clones that routes to the dev-routes you need