BIRDs allowas-in functionality

[Bartek Kois]

Hi 
I`ve got two networks in different locations without any connection between
them. In each of them I`ve got two BGP routers connected to two separate
ISP`s. Both networks have the same AS number but their BGP routers propagate
different prefixes (different /23 prefix for each network). The thing is
that hosts inside one network don`t see hosts in the second network, because
of BGP anti-loop mechanism.
Typically this problem can be solved by using "allowas-in" directive. How to
achieve the same functionality in BIRD configuration?

Thanks for any help.

Best regards
Bartek