Couldn't you just use a full BGP feed from a provider and configure your
inbound route-map/policy with the necessary parameters to obtain the part of
the BGP table that you want? Or if this is just to populate something in a
lab with a specific set of BGP info, you could obtain a copy of the table
from someplace like route-views and load up the lab router or MRT (or equiv)
in the lab and massage the table data within the lab.
If this is for a customer/production router, I suppose you could coordinate
with the upstream provider to do something similar with their outbound
route-map/policy so that you only get a partial table.