multiple routing tables for internal router programs

[Andrea <andang76@gmail.com>]

Maybe a strange request, I'll try to explain this as clearer as I can 
(forgive my bad english, please :-) ).

I'm setting a linux box as a router. My router uses multiple routing 
tables, so I can address the traffic from specific ip addresses of my 
lan to distinct ISPs providers (specifying a different default gateway 
fo r each table), marking packets with iptables (prerouting marks).

This works with the forwarding traffic (lan-ISPs) that crosses my router.

But how can I reach the same result for programs that are working INTO 
the linux box? All I want is that a program (ping, for examples, or a 
VOIP server, better) uses a secondary routing table in the same machine. 
In this mode, I can manipulate route settings for different classes of 
program in my router.

Is it possible?

Thanks