[c-nsp] Suppressing/Over-riding Longer Prefixes

[f287cd76 at opayq.com]

Hello All, and Happy New Year.
I have two large sites, each connected to a different ISP and receiving full BGP routes.   
Each site announces only it's own prefixes during normal operation. Our goal is to keep traffic local unless there is an outage or other event. We set a high WEIGHT on each of our edge routers.  This serves to keep most traffic local to that site and not use the IBGP connection between my sites. 
As expected, there are some inconsistencies between the routes learned from each provider.  
In particular,  Provider A sends longer prefixes for some AS's than Provider B does.   For example .. Provider A  may send two /24 while B sends /23. 
Much of this is random, and for the most part isn't an issue other than the asymmetric routing.
But there are some business partner AS's I'd like to over-ride and force their traffic to use the local ISP as much as possible.    No point backhauling it to my other site. 
Weight, Local Pref etc won't work for this as the longer prefix usually trumps all other policy... at least as far as I know now. 
Looking for suggestions on how to influence routing to do this.