[j-nsp] Transit only to some ISPs

[Raniery Pontes]

Hello,

   I´m looking for hints on what to do in the following situation. 
Suppose you´re an AS "A" with two upstream providers "COM" and "ACAD", 
running only J boxes. Upstream COM announces full routes but upstream 
ACAD sends you only some "special" prefixes.

Most customers in AS A have full transit to both providers COM and ACAD, 
beside common transit to other customers inside AS A.

Now, suppose some new customers (inside AS A, no BGP with them) should 
get transit inside AS A *and* to upstream ACAD *only*.

What would be an scalable and elegante way of doing this ? MPLS/VPN´s ? 
Source-routing ? Anything else?

I´m more concerned in finding what to do instead of how to do.
But full config examples would be accepted ;)

Thanks

Raniery Pontes