on cisco
The neighbor allowas-in command allows you to disregard the rule where we will not accept a prefix if we see our own AS in the AS-PATH.
how to in mikrotik?
There is allowas-in peer parameter in version 4.
See:
http://wiki.mikrotik.com/wiki/BGP#Peer
http://www.mikrotik.com/download/docs/bgp/3-as-hacks.html